Trade Rondo something like Collison, Hibbert, and George (frankly I'd do this regardless of any other moves)
Trade Garnett something like this Hinrich and Josh Smith
Trade Allen something like this Korver, (Asik and Bogans for dollars), 1st, future 1st
Trade Pierce something like this Kaman, Aminu, Minny 1st (top 3 protected as I think that is the only way LAC would agree to give it up)
Now is the time to start over. It is apparent the Celtics only shot of competing long term is to go into full bore rebuilding this year to try and utilize the assets and get as many draft picks and young players as possible.
This year the rotation would be with those trades (late lottery type team)
PG - Collison, Hinrich, Bogans
SG - Korver, Hinrich, Bradley
SF - George, Aminu
PF - Smith, O'Neal
C - Kaman, Hibbert, O'Neal
Going forward you let Kaman, Hinrich, and O'Neal walk and plug in the two or three rookies from this year into the lineup in positions of need. The C's should be able to get 3 or 4 solid players (hopefully Minny is bad but not that bad and the Celtics hit in the lottery), at least one of which should hit given the depth of the draft to pair with Smith, Hibbert, Collison, and George (even Aminu looked pretty good as a rookie last year). The Celtics would also have cap room to add in someone else next summer.
I am only half in jest posting this, as I think if the Celtics don't go all in right now they really should start the rebuilding train. I don't know if any of those trades are doable or enough value, but it is those type of trades I'd be exploring hard if I'm the Celtics right now.