DIY GoPro front protection without case?

[Explorocam]

I now have an extra GoPro Case, I'd like to make something like layer lens with the case. Anyone have any ideas, pictures, instructions? I'd like to make my own so I don't need to spend the extra cash and wait for shipping.

Can I just use the front part of the case by cutting away the rest of the case? Any ideas, Photos, instructions?