Here's one with an 8-1/2" in cutout: http://www.beckson.com/screwout.html

To seal the deck after enlarging the hole, use a dremel tool, or simply a use a gouge or chisel to remove about 1/2 inch of the core material between the layers of glass. Then fill the resulting void wit putty made from epoxy resin and cabosil.

If the deck is solid glass, not cored, you don't need to do this procedure.

Don't forget to seal the deck plate ring

Kevin