That was such fun that I designed another one. This is one that could be done with a single "through the bottom" bulkhead overflow drain. It is a bit wild, but I do think it would work and be safe.
(Mind you...if something blocks your only bulkhead, you've got a problem whether you've done this mod or not!)
Untamed Mod II:
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400 gal reef. Established April, 2007. 3 Sequence Dart, RM12-4 skimmer, 2 x OM4Ways, Yellow Tang, Maroon Clown (pair), Blonde Naso Tang, Vlamingi Tang, Foxface Rabbit, Unicorn Tang, 2 Pakistani Butterflies and a few coral gobies
My Tank:
http://www.canreef.com/vbulletin/showthread.php?t=28436