Cutting footpockets

[Mermaid Tula]

So I was reading about someone cutting the footpockets of their Oceanika fins. I was wondering if anyone has done this with a Finis Foil. My foil isn't quite fitting me at the moment. I've tried heating it to stretch it out, but I've had no luck. I saw the tutorial for using ice to stretch, but I don't think that will work for such thick rubber.

So if anyone has had any luck cutting the footpockets of their finis foil, or know if it would work for the foil, I would be grateful for any information.

Thanks!