Hi fjfa.
There's a number of Java scripts that can help you do that.
The hard part is to get the Java selection added to the cart, but as you say - there's no contrib made for that (yet).
If you look at the source here:
http://www.plexiglas-shop.com/DE/en/cutter.htm?$product=foxtncj6077%7Ep&comeFrom=detail
then you'll find a working Java...