Its a little confusing by the words you are using. If you are making a nosecone plug out of MDF that you are going to make a female mold of, this is what I would do.

Sculpt the mdf bd close to your final shape. Stay below your actual finished surface. Now put a resin rich layer of glass matte (polyester resin) to seal the wood. Once cured lather on layers of bondo (auto body filler) and carve with a cheese grater (slang for auto body file).

Continue until roughed in and then start to sculpt with board sanders. Prime and sand. Continue until the nose plug is perfect and shiney.

Now you can talk about pulling a mold off of the plug.

Wax PVA and so on.

Hope this helps.

Fred  

Hey,