So, I've been thinking of this for quite a while. Every time I try to build a decklist for this deck, I find myself overwhelmed by amount of choices and I've came to conclusion that it depends heavily on which other decks you are supporting. So, I've put together the core "glue" of this deck, which then can be enhanced by additional elements, depending on the other decks and current quest.

This support deck will work best in 2-3 player game, but note that it can't pull it's own weight - you'll need some heavy forces of other players. All this deck will do is make your existence as comfortable as possible.

Heroes:

Glorfindel(Spirit)

Aragorn(Lore)

Boromir(Tactics)

Core Allies:

Minas Tirith Lampwright x3

Core Attachments:

Palantir x3

Core Events:

Desperate Alliance x3

Here how it works. You need to get Palantir as soon as possible. Mulligan for it, if needed.

Attach Palantir to Boromir and get scoutin'. Boromir can ready himself if needed later. With this, in 2-3 player games you'll almost always know what's waiting for you during quest and can prepare accordingly. Surges will be mitigated by Lampwright, because you'll know what they will surge into most of the time. As you might have already noticed, this deck will build a lot of threat real fast, hence the Spirfindel for low starting threat and Loragorn for the threat reset when it reaches the boiling point. And if someone else reaches dangerous threat level - you lend them some Loragorn for a refresh phase, if you catch my drift.

Now, let's talk a bit about some cards that can be universally added to this deck.

Suggested Allies:

Envoy of Pelargir - can give another player a resource and does not requires a resource match, which is a big plus in a tri-sphere deck.

Miner of the Iron Hills - if any nasty conditions are present.

Silvan Refugee - good and cheap questing power. Plus, with the knowledge you posses you'll know for sure if they'll survive the questing phase or not.

Vassal of the Windlord - in case some of the allies having any trouble clearing their engagements.

Longbeard Elder - you'll always know to trigger his ability or not. Thats in case any of your comrades runs Leadershit, of course.

Suggested Attachments:

Ancient Mathom - in multiplayer there'll usually be a location to explore around. 3 cards won't hurt, unless you're facing men of Dunland.

Asfaloth - need I say anything?

Elf-Stone - putting costy ally into play for somebody? Even better.

Gondorian Shield - will make Boromir good defender against the hordes.

Light of Valinor - to make Glor quest, obviously.

Protector of Lorien - to get rid of excess copies of Palantirs and etc.

Spare Hood and Cloak - Boromir can ready people with this thingy while remaining ready himself.

Thror's Key - useful and cheap.

Thror's Map - also useful and also cheap.

Suggested Events:

A Test of Will - no comment.

A Watchful Peace - will cycle a harmless location back, and if it stick - it will give you sorta safe guess for your next Palantir usage.

Daeron's Runes - find the cards you need fasta.

Deep Knowledge - everybody getting two cards is a nice feat in multiplayer. Watch your threat though.

Elrond's Counsel - will help you to keep your threat a bit lower than usual right off the bat.

Expecting Mischief - you already know what to expect, so just fire away!

Feint - to feint.

Hasty Stroke - to stroke hastily.

Peace and Thought - consider this card carefully. Remember that Boromir can always be readied.

Power of Orthanc - to get rid of some conditional nastiness.

Possible Hero Alternatives:

Spirfindel -> Fatty Bolger. Negating some strong-threat foe may be crucial sometimes, but your threat will grow even faster.

Spirfindel -> Eleanor. In multiplayer, treacheries usually more frequent and more devastating, so this girl might be of use.

Loragorn -> Denethor. With the knowledge of Palantir, you might send something extremely nasty back to bottom. Or, if Denethor remains ready at the end of the round, you can scout for the first card of the encounter deck for the safer Palantir guess. Watch out for your threat, though. No reset means playing really fast or really cautious. Or both.

Shadow of the Past would be a decent replacement for A Watchful Peace. It's neutral and can move any card type, though it does cost another resource.

Glorfindel can be swapped out for Eleanor if scenario has some particularly nasty treacheries. It will cut off Asfaloth and Elrond's Counsel though.

Very different take on those three heroes. I like it. Just to play Devil's Advocate, it is likely that whoever you are supporting (unless it's you) will be using one of those heroes!

I won't comment on the cards because as I look at the list I start warping it into my super-hero attachment deck and that's not what you are trying to do.

I tried something similar in the past.

Had lore & spirit only though.

Used Fatty threatty with song of earendil to eat the other players threat raises; and he could also eat some threat from the staging area at critical points. Then I'd reset with aragorn when getting high in the 40s.

This combo would work well if you'd get song of earendil out early, then using deep knowledge for 2 cards each, and eating your mates threat to boot.

I also had elf-stone & ancient mathom in there. Both are great utility cards if you ignore the stupid table talk rule.

Last thing I can recommend is miner from the iron hills. This guy is a winner in encounter decks with condition attachments in it.

Power of Orthanc is a star in this type of deck. Free to play essentially and Strider will take care of Doomed in the end.

Just to play Devil's Advocate, it is likely that whoever you are supporting (unless it's you) will be using one of those heroes!

This can be easily solved by building your decks collectively.

A little update. I totally forgot the Longbeard Elder. Also, added alternative heroes section.