it's in section 64 of the CBA FAQ:
A team is not permitted to stretch the team salary charge if in any future season the team salary charges for all the team's waived players would add up to more than 15% of the salary cap for the season in which the player is waived. For example, if a player is waived in 2011-12, the team cannot elect to stretch the player's team salary charge if the sum of the team salary charges for all of the team's waived players in any future season would exceed $8,706,600 (15% of the salary cap in 2011-12).
http://www.cbafaq.com/salarycap.htm#Q64
the question I have, as a Blazer fan, is if the "all the team's waived players" stipulation includes players waived under the amnesty provision. I suspect it probably does which would mean Portland can not gain any cap-relief from the stretch provision until Brandon Roy's amnestied contract expires.
but maybe I'm reading it wrong?