Okay, I think I can create the fire mode selector by milling a hole through one half of the socket of where the pin that the sear rests on. Then I'd use a nail in place of the pin. When I put the nail in, I get semi auto, and when I take it out, I get full auto. Since the nail is pointed it will be able to fit in. I have youtube links btw:
YouTube - Tippmann 98 Custom Full/Semi Select Fire Mechanism Video 1
YouTube - Tippmann 98 Custom Full/Semi Select Fire Mechanism Video 2
YouTube - Tippmann 98 Custom Full/Semi Select Fire Mechanism Video 3