D69 and I had a similar discussion just the other day. You can make the trade on Draft night but not execute it until July 1st. That way, Portland could make a deal with say the Cavs who would lose Deng, Spencer and Miles off their cap thereby being able to absorb Aldridge. Now Portland would have the cap space to go after someone like LeBron if for some fluky reason he wanted to come here and he would join Lillard, Nic, #1 pic, Lopez and likely other assets/picks acquired in the Aldridge deal.
Not that anything like that is going to happen....