BTW, playing with the ESPN trade machine, I noticed that Portland has a sizeable trade exception.
The following three-way trade works, per the TM:
Portland receives Tony Allen from Boston (using TE)
Knicks receive Sergio Rodriguez from Portland and Brian Scalabrine from Boston
Boston receives Chris Duhon from Knicks
Not sure whether that's something that everyone would agree on, but thought I'd throw it out there.