Do what I did. Use both of your drilled holes as drains and return over-the-back.
I use a very narrow across-the-back calfo-esque weir. I took out the bulkheads to make the drain holes bigger, and siliconed boxes on the outside of the tank (analogous to the outside box of a U-tube siphon overflow).
pics of mine are on pages 2 and 14, with a good graphic on page 20
http://archive.reefcentral.com/forum...5&pagenumber=2
If this seems to involved, or if the tank is set up already, go with your idea, but use both holes as corner weir drains, not just one, and return over the back.