Mount the servo on both mounts, then screw the mounts onto only one hole. This will let you locate the other holes position. Use a pen to find the spot, take it all off, then use an exacto knife to drill a small hole on the spot. Then use a drill (drill press prefered) to make the hole and counter sink.

You can also try to open up the servo mounting tabs a bit and use a washer on them.

Hope this helps.

Sands