Wooty! Welcome back Kotter.
I would do something like what I did for my FW tank (
http://www.canreef.com/vbulletin/showthread.php?t=28505)
Although instead of the external Durso, you could just have a strainer in the box. One thing about the external Durso I did, I didn't give myself enough space for a strainer and I did get a few smaller fish find their way down into the sump (since it is a FW tank, they found filter floss and bioballs - didn't exactly live through that ordeal
). But a corner cup overflow would work on your tank, Durso or otherwise.
Or heck, do coast to coast! Leave it with the one hole, or drill another on the other side.
Or just patch the glass ... at the top it's not going to be exposed to too much head pressure so just a 1/4" patch of glass would do the trick. And then you could do whatever ...