Actually I texted my friend about this and she says Gary Sinise is down for Dr McCoy
She also said Robbie Williams was down for Captain Kirk but not the pop singer Robbie Williams. However I did a search on google about this and although the Gary Sinise rumour comes up the Robbie Williams rumour only seems to refer to Robbie Williams the pop singer and definitely isn't true.
The only actors listed so far on the IMDB site are Leonard Nimoy and
Zachary Quinto