I'm going to run the Target of Opportunity side mission tomorrow for my group. The Rebels have done really well for themselves the past two missions and even geared up really well, so I'm looking for any tips you can give me to avoid being steamrolled in this mission. I do not want to give them those Rebel Saboteurs, who I feel are the best threat-value ally available to the Rebels.

It looks rough.

Once the door to the archive is open you need to be two Royal Guard attacks away from wounding all the Rebels, otherwise it will probably be over with one more Rebel activation.

Obviously you have to A: Delay the initial terminal interaction as long as possible and then B: Burn down the Saboteurs asap.

I think A is pretty much impossible, but B should be relatively easy to do. I'd go with Trandoshans and a (elite) Nexu as your open group, just murder and block the Saboteurs as best you can until they are 'defeated' and hope it's then too late for them to open the door in time with only 1 action a round.

Focus on the saboteurs. Without them its almost impossible for the heroes to break the door, especially if you're still early in the campaign.

I agree with Rumblefish that Trandoshans is a very good group for this mission. Their ability to give strain on targets 3 spaces away is a guaranteed damage on the saboteurs. Coupled with the extra damage when adjacent, if you can manage to place your figures correctly you can kill one saboteur per round with the Trandoshans alone.

I found bringing a Nexu helped a lot, blocked corridors and meant extra movement points to get past him only for him to pounce over them again and attack