Chris

It might help to use a dam in the hole so you can release the part easier. When you lay up, take a small piece of sealant tape, and put it in the middle of where the hole is, on the mould face. Continue the layup and apply your breather stack, making sure you make holes in all of the layers so that the tape can poke through. When you bag up, make sure the bag touches the tape. This will essentially creates a hole that will make release very easy.