I have seen a lot of different methods of attaching rails to 2nd gen Glocks. Unfortunately I have yet to see one that would be considered remotely acceptable. No matter what, they look like and afterthought and therefore in my opinion are unacceptable.
My advice, sell the one you have and purchase the one you want. Do not settle!
FYI: You can not cut a rail into a 2nd gen Glock because it is already smaller than the FGR pistols. (example: I cut it twice and its still too short)