I think i know what you mean bigwheel... but I don't see how that would work, wouldn't that make a hole too large, so that his sub actually fell through them? Forgive me if I misunderstood.
the owner of the sub says he wants to flush mount, meaning that there will be another piece of board material, which the sub will be mounted to. Then on top of that piece will be the piece that makes the sub flush with the box...which is the same diameter/cutout as the sub itself...