Someone else here stuck some wooden blocks under the screw holes. They drilled a pilot hole through the middle of a block of wood (suitable for the mounting screw you are using), then ran some nylon line through the screw hole, out of an F-hole (or through the bridge pickup hole might be easier), then through the wooden block and tied a big knot on the back so that it could be dragged back through the body. Used glue on the upper surface (not sure what glue but epoxy should be nice and strong and also gap filling), then pulled the block up tight against the body and managed to keep pressure on the line until the glue set. Then repeated for the other screw hole. If you don't cut the nylon line short but leave it long behind the knot, then you can leave that end out of the guitar body and easily pull the line out again in one piece. easier than cutting the line and then trying to shake the knot out of the body.

Then once you screw the screws in again, they've got a lot more to bite into, plus the screw keeps the block pressed against the top so it doesn't move.

As Shazz says, I'd also use different mounting screws, not ones with an unthreaded section at the top.

I know it's a bit of a fiddle, but it's not too difficult (more time consuming) and will give you a far more solid trem mounting.

I'm not familiar with the supplied trem, but from the kit picture on the PBG web site, it doesn't look as if anything else but bending it will do the job. Although if the height of the trem bar is determined by the length of the spring, then cutting the spring down a bit might help (again, I'm sure I've seen someone else do this recently).