This has nothing to back it up, but I seen this on another web site, so take it for what it is worth, it stated:
"According to a poster on a Bills forum that I frequent, last night at the Bills Booster Club meeting, Bills GM Tom Donahoe confirmed that the Bills will wear "throwbacks" for two games this season.
Evidently, he said that they do not need permission from the NFL, as two games do not require it, but three or more do.
Two games mentioned are the home opener vs. Houston and the game vs. San Diego.
Said that the unis need more "tweaking" before they'll be made public."