This is more of a mental exercise than an actual practical question.
The language of "cannot" on the contracts appear only on the front sides of 3 out of the 4 known contracts. The Grey Wanderer has to do with choosing heroes, so I am going to disregard that one. With The Burglar's Turn and Forth, the Three Hunters, the restriction of the deck are on attachments and allies, respectively.
Once the card is flipped, this no longer applies, correct? So if you can somehow manage to get attachments/allies into your deck, it is perfectly legal at that point, correct? Some "message from elrond & drinking song" combo, or something?