You should be able to practise on any number of scrap plastic pieces that may be lying around. I already have some ideas for tools to use for making the cuts. When I have the chance I'll go out and get one of them to test. So far all my best ideas involve melting plastic unfortunately - something I hate doing because it's tricky to get just right. Then there's the route with a rotary tool and a fine bit. Obviously the most repeatable/easiest thing to do is to have a mold with the proper design already.

Bruno