with Boston as a FA, is is able to do so. Typically, the reason why teams do sign-and-trades is because they lack the cap space to sign the players outright. Doing the trade allows them to both shed salary as well as acquire the Bird rights to the player immediately.

In this case, I don't think Boston would agree to a sign and trade because it doesn't benefit them at all. The only way it really benefits them is if that is the only way that Gordon will agree to go to Boston.