Hi I have a ice hockey boot that I'm converting to quad skate. The boots sole has a large holes in ball of foot an in heel. I want to fill the hole in to make sole stronger when the plate/ wheels gets bolted to boot. 

The hole depth is 8mm in depth to make up . What is best way of filling hole in....layering up carbon fiber or is there a light weight foam core that can be used?  If there is a foam core is it suitably strong if i needed to put bolt through compression wise?
I was then thinking a layer of carbon fiber across whole sole to tie it all together.

Thanks for any help and advice.