Hi again
It's quite funny, I am jumping the optik illusion with a Sony hc-96 on the top, which is obviously the same setup you have thought about getting. You have to keep in mind that the hc-96 it's a quite wide camera (72mm). At first I did sidemount mine, but only for a few jumps, then I put it on the top in a box from Bonehead, (think it is the "i" model). A good advise however is to talk to the local a local cameradude with experience, before starting to drill holes in the helmet. Another good advise would be to perhaps borrow a helmet and try to jump with cameragear for a few jumps, just to see if it's really something you want to something about. After all cameragear isn't for free.
Henrik