All data from Sham.
Spurs have $41,666,028 in committed salaries (TP, TD, Diaw, Bonner, Green, Leonard, Decolo, Mills, Joseph, Baynes)
Spurs have $30,642,049 in cap holds for Manu, Tiago, Blair, Neal, and LJC's rookie scale slot. (not counting all the cap holds for the ghosts of Robert Horry, Nick Van Exel, etc..)
Spurs current salary cap figure is $72,308,077
1. Re-signing Manu adds $6,746,988 to salary, removes $19,136,250 cap hold. Cap figure would be at $59,918,815; $1,239,815 over the cap.
2. Renouncing rights to Blair, Neal and getting the agreement with LJC that he's not coming this year removes $4,012,199 of cap holds. Spurs now $2,772,384 under the cap.
3. Amnestying Bonner would remove $3,945,000 of salary, but add a $490,180 cap hold because the Spurs will have fallen below the 12 player roster limit. Spurs now $6,227,204 under the cap. Probably not enough to get AK. Definitely not enough to get AK and $2 mil for Pendergraph.
4. The Spurs could salary dump DeColo. Subtracts $1,463,000 of salary, but adds another $490,180 roster charge for falling another player below the 12 player limit. Spurs now $7,200,024 under the cap. Probably getting in the ballpark for AK, but still not enough to get AK and pay $2 mil for Pendergraph.
5. The Spurs could salary dump Mills. Subtracts $1,133,950 of salary, but creates one more $490,180 roster charge. Spurs now $7,843,793 under the cap. A little more money to work with, but still not enough for AK & Pendergraph.
6. At this point, what's the point? Salary dumping Joseph is only going to get you another $700k or so because the Spurs would get hit with another roster charge. $8.5 mil of cap space is probably the salary AK is hoping for, and that still doesn't take into account Pendergraph. Not to mention the Spurs will have had to dump 6 players to get here, with having to orchestrate as many as 3 separate salary dump trades with 3 separate teams. Way too complicated to put it all together, and probably not even worth it at this point.
Conclusion: The Spurs aren't getting AK by signing him outright. It's S&T or bust. Since it's S&T or bust, there's really no point in trying to get under the cap.