GRP nosecone recess

[alga]

I've decided to give a shot at making my own GRP parts. It might be a mistake, but I started with the nosecone. I plan to do the male-female-male process, starting with an EPS and taping compound buck. Now, do you have any ideas how should I go about the recess for the bonnet? If I just carve it into the buck it will make separation troublesome if at all possible, won't it? My current working idea is making the mould a bit longer, then sticking the recess in the mould out of plasticine, or some kind of adhesive plastic strip. Then it would be removed from the mold along withe the finished nosecone, and would have to be redone when making another part. Any better ideas? I'd really like to stick to a one part mould for my first GRP fabrication.