Here's what I think the Spurs did. A 3 year deal starting at full MLE, totalling $15 mil with a partial guaranteed 3yrd year would look like this.:
Yr 1 - $5.854
Yr 2 - $6.322
Yr 3 - $2.824 (the guaranteed portion only)
Total - $15.000
But the Spurs could have told Dyess they needed to save some of that MLE for Blair and then offered him a 3 year deal starting at something less than the MLE that would still net him the $15 mil over the 3 years. That would look like this:
Yr 1 - $4.630
Yr 2 - $5.000
Yr 3 - $5.370
Total - $15.000
This would save the Spurs around $1.2 mil of their MLE and guarantee Dyess his $15 mil, but Dyess would be taking a hit in years 1 and 2. However the CBA allows teams to take 20% of the contract value and pay that in the first year as a signing bonus. I won't get into all the mumbo jumbo on how all that works but you can read about it here.
http://members.cox.net/lmcoon/salarycap.htm#Q62
What it ends up working out to is that Dyess would actually be cashing checks as follows.:
Yr 1 - $6.630
Yr 2 - $4.000
Yr 3 - $4.370
Total - $15.000
Even though Dyess would end up recieving more money in the 1st year than the actual MLE, it works because the CBA states that a player's cap figure is equal to the amount he earns, not the amount he gets paid. There's a distinction here because Dyess is in essence getting paid money in the 1st year that he hasn't actually earned yet. But he doesn't care and the Spurs are okay with it because it allows them to save some of their MLE. It's win-win. This couldn't have happened without Dyess agreeing to it so we owe him our thanks.