if you can somehow find the specs for OEM FD studs, you'll know.
knurl diamater is about all that matters, and its .509" for the FC. good luck finding FD info..

 

There's also some Miata metric studs that could fit, they come in a larger knurl diameter. If you find one that's bigger than the FD size, you could always drill your hubs to accomodate it.

 

And throw the centers off

 

Well obviously don't just get a hand drill, it's something that should be done on a milling machine with proper care to make sure that the holes stay centered. There's no reason it can't be done, you've just got to do it properly.