Starters:
PG: Rondo
SG: R. Allen
SF: PP
PF: KG
C: Perk
2nd Unit:
PG: Andre Miller (Via S/T, Scal, T. Allen, Pruitt, pick if necessary...expirings, saves them cash)
SG: E. House
SF: B. Walker
PF: Hakim Warrick (LLE)
C: Sheed
3rd Unit:
PG: E. House
SG: JR Giddens
SF: H. Warrick
PF: Powe (Mid-season signing after injury)
C: Robbert Swift (handcuffed to the bench)
I think the sixers do the above trade based on their knowing they are far from contending, and can shed additional cap. If we are able to get a guy like Warrick for a one year LLE I think he goes for it. He only made a couple mil last season, and I think is one of the more under-rated defenders in the league. He's been on a terrible team his whole career, and one championship run with the C's will net him a bigger contract in 2010. He would fill in nicely as a backup for KG, but Warrick can also be platooned with B. Walker and Giddens to give Pierce a rest (especially against bigger 3's like Lewis, Artest, Granger, etc. while using Walker against the undersized types like Deng).
The obvious question mark comes at the Center spot. Personally, I think the only thing to worry about is injury at this point. Between Perk and Sheed, I think it will be more of a fight for minutes anyway, so if neither of them go down, we are good. Then you can also hope for Powe to somehow find himself back in the mix.
You asked for desirable, and I also think this is reasonable for these two moves to be possible, although I doubt they both happen (which sucks).