Your best bet is to drill the tank. There are some creative ways to do this and it doesn't have to cost a lot of money. If you need the name of someone who can help you with this, let me know.
The other way, and to answer your question, is here:
http://www.jlaquatics.com/info/89/Ov...%26+Sumps.html
Take a look at the CPR C-Siphon Aquarium Overflow.
If you've never dealt with J&L, you'll have lots of fun browsing their website.
- Brad