Cut foam to fill ding

Hi everyone,

I picked up a ding in my favourite board and would like to make the repair invisible, so don't want to use q-cell filler.

I want to cut some foam from a blank (that I have), then glue that into the hole instead of filler.

What's the best way of going about this? Obviously I need to make the foam piece match the shape of the hole in my board.

The ding is right on the esge of a fish tail, so ideally I want to the keep the repair as small as possible (so as to not mess the tail's shape).

Have added a pic to show what I'm dealing with... should have used a scale at the time to show size!

Thanks very much,
Lewis.