I've mentioned this idea in replies to threads, but I don't think I've actually started a thread on it.
The Jazz have Enes Kanter, 7'2" rookie Rudy Gobert, and Derrick Favors in the big man rotation. That's three guys who can play center. Favors is the power forward. The back-up behind him is combo forward Marvin Williams, who seems like more of a small forward. The Jazz also have Andris Biedrins from Golden State. It would make sense for the Jazz to swap Biedrins for a back-up power forward.
The Celtics have extra power forwards.
Both Kris Humphries and Andris Biedrins are expiring contracts who are not in their teams' long-term future plans. Humphries is set to make $12 million. Biedrins is set to make $9 million. Coincidentally, teams are allowed to send out up to $3.2 million (total for the year) as part of trades. Unfortunately, teams are also capped in how much cash they can receive in a year (the same amount) and the Jazz already received cash considerations from Golden State. Otherwise, Humphries and cash for Biedrins makes a ton of sense for both teams, although Utah should try to get something else like a draft pick out of it.
Still, Humphries for Biedrins works under salary cap rules. Additionally, the Jazz have a little bit of cap space they are trying to auction off. Humphries, Crawford, and a first (likely Brooklyn's 2014 pick) would seem to amount to the Celtics selling a first for $6-8 million ($5 million in salary savings plus an addition $1-3m in luxury tax savings). If the Celtics explored the deal, Ainge should try to get one of those second round picks coughed up by Golden State.
I'm not sold on the idea of using a first-round pick to get under the luxury tax (or, at least, I'm not sold on doing it right now when there is a decent chance the Celtics can wait until the trade deadline and find a deal to get under the tax threshold), but I think Humphries for Biedrins is an idea that should have both teams being willing to negotiate.