From out of left field but really not that crazy how about this?
Dwight Howard and MWP for KG and the Captain.
Why for Boston? Sends Pierce and KG to a city they like for their own reasons and brings back a guy who is possibly a franchise center. KG and Paul continue to battle together along with some old rivals and take on the young champs and RAY one or two last times.
Why for LA? With a decent coach you would think that could be the best half-court lineup going. LA does not worry about rebuilding when its over because with cap room they seem to get their guys every time.
Boston is instantly rebuilt waiting for a few young guys to develop to seriously be in the mix assuming good health for a bunch of guys who have had serious injuries. Howard, Rondo, Sullinger, Bradley, Green, Wilcox, Barbosa and a few guys who have been actually healthy Lee, Terry,Bass, MWP
Dwight can get all the shots he could want with no other volume shooters on the squad and this team could play very good defense.
Why not for the Celtics? Sending the faces of the franchise to the Lakers! I would seriously have to not hate the Lakers for a few years.