Some of their bikes i noticed come with a FSA conversion headset. At least thats what it said in the brochure. There may be others. I have bought a rush frameset and am going to use my fork so yes, no big deal.
Just search on eBay for a HeadShok adaptor headset. Cane Creek makes some nice Headsets converters with sealed cartridge bearings. Just check your manual to figure out what the maximum fork length should be, and that's it. Problem Solvers makes an adapter kit which consists of 2 cnc'd rings which fit inside your existing HeadShok bearing cups, but then you still have to buy another, "regular" headset. I would either get a cane creek or a fsa since they look the cleanest. If you're not sure, your cannondale dealer can order the right one for you too.
Here's a pic of the one I used on my "old" Prophet. (Which I'm currently trying to sell on eBay by the way )
"Common sense isn't always that common!"
Custom Prophet and Custom Delta V