Anyone build a Hang On Overflow??

[200gal]

I am wondering if someone can give me any good ideas for building a hang on overflow. Plus what experiences they have had with them. My tank has a 3.5 inch glass brace around the top of the tank so I do not think a manufactured one will fit. Just that my tank is full and not enthused about emtying it to install an overflow. Has anyone had any success or failures with drilling near the top of a nearly full tank?