I've been in your situation before, and I know the dilemma you face. One thing you might try is going to Bobby and running a few pages from your site through it using the 508 filter, which they recently implemented. It's excellent, and the comments are probably the most useful part. Since Bobby is checking for 508 compliance, questionable items it reveals may help your cause by showing people in your organization just how detailed the 508 spec is, and that it's not something they can just blow off.
Best of luck!