your g/f sounds pretty handy! though i'm not sure if that's a good solution or not, maybe try it on a spare piece of foam.
my pelican case came with the pick n pluck shit, and for parts where i wanted 1/2 height, i took a big section of foam, and gently sawed it in half using a very very sharp cutco knife. it came out kinda jagged but that side faces down and the good clean side faces up.