If I'm not mistaken (and I frequently am), I think Bonner's Bird rights would let the Spurs do the same thing they did with Manu, which is to sign him for money that puts them over the cap. (Or more than the min, if they're already over the cap.)
I honestly don't know where the Spurs are vs. the cap right now, so I don't know the exact dollar number they would have to pay Bonner to make the salaries match. It wouldn't have to be exactly the amount Smart is getting. But Smart is making about $3.5M, so if they signed Bonner for that amount, I don't think there is anything that would stand in the way of the teams swapping those two.
Bonner has Full Bird at this point, so a 1-year deal would mean that he couldn't be traded with out his consent. But he wants to go to Boston, so that wouldn't be a problem. I don't know... I think it works.
BTW - throwing in Mills would totally defeat the purpose. I'm looking at PG insurance, and maybe a change of pace player for specific situations - with a bonus if Chip could help him with his shot. Losing Mills to gain Smart would be a bad trade.

. Who gives a , there's millions of good guys out there. I'm almost certain this has RC's nudes
