Could you not, perhaps go the route you suggest, getting the main hull glassed in as far as possible while retaining flatness, fill coats and all.... Then feather off and then try the taping of the insides with bias cloth cut in a sort of oval so that you can get to the edges in the recess for fairing in?

If it works great, if it doesn't then pull the tapes out while they are still wet and go back to plan A.

I think if you experiment with a few shapes for your end tapes you will be able to find a shape that allows you to get to the edges for feathering.

Et