A reasonable solution to levelling is to machine a pocket to suit your board size in some scrap MDF, and fix your PCB in it. If you are doing large PCBs, I would have them made as cutting off copper is a slow business.

Then again, if you are anything like me and only find your design errors when testing the built circuit, if you have cut your own board there is less intensity to that 'Oh F***!' moment.

Rob