I think I read that you could do this in 2006 during free dining. Was it allowed in 07? We are going in Aug 08 & don't want to use all our ts as we found it took too much time last year.
2006 was a messed-up year, in which Disney very much oversold Free DDP to a clientele of visitors who had no clue they needed ADRs to eat TS meals. In order to keep the food riots within manageable levels, Disney offered a menu of options to trade in unusable TS credits for CS credits and "stuff."
In 2007, they offered far fewer Free DDP packages and had no such problems, so I would not expect any similar offers in 2008 when the offerings are even further reduced.