You have two options, both requiring some tools...
The first one is to use a dremel with the smallest diameter cutting wheel you can find. Dremel a slot into the screw head and remove the screw using a normal flat blade screwdriver. You do need a fairly small wheel though otherwise it will be difficult to cut a deep enough slot without cutting into the chassis.
The second option is to drill the screw out using a pillar drill. If they are M3 screws, drill them first using a 2.0mm drill then a 2.5mm drill. The screws will usually collapse and come out with the 2.0mm drill, leaving a nice clean hole. You will need a pillar drill though, a hand drill won't do the job.
RC-Timing Software - http://www.rc-timing.com
Mercedes AMG F1 - http://www.mercedes-amg-f1.com/