So, to be more precise -- you have rounded off the phillips head recess on the screw?
If this is the case, then you can drill it out. Fine fiddly work, to be sure.
http://www.harborfreight.com/13-piece-left-hand-drill-bit-set-95146.htmlIf you go there, consider using a left hand bit to do the head drilling. It offers the advantage of when the screw loses clamp tension between shank and head, the left hand direction of the drill bit instantly backs the screw out of the hole, preventing you from doing a drill through error.
Some have had success putting a slot in the screw head and using a flat blade, others have reported using a pair of vice grips with a needle nose configuration that can get down to grip the screw head well enough to back it off.
Good luck with your repairs, and remember -- that diaphragm-slider assembly is worth nearly $170 to Suzuki when you go to buy one.
Paying a competent, well equipped dealership mechanic $15-20 to get the damaged screws out might not be a bad idea
as long as they will stand good for their goof ups should they screw it up.