There are lots of ways you can do it. The foam I use on my full scale Long EZ would be ideal but you might not want to buy a huge chunk of it. It is high density foam and you could put that on the nose and sand a good shape, then glass it and take the foam out. If you just use white bead board foam, gas will eat the foam out like you said. Harder to get a good shape with it though. You could use a wood block on the front and sand your shape out of it. Glass it and remove the wood from it.

To remove anything from the inside, wax whatever you use as a plug well. I would use many coats. I use PVA mold release in my molds too, then wax with a good paste wax a few times. Make sure there are no holes. Glue will get in them and make it stick more. Once it is waxed really good, you can glass it with really light glass, maybe 4 layers of .5 oz cloth for a cowel. It will be thin, but you don't want too much up there. You could do heavier if you need nose weight. Remember to make the plug just a bit smaller than you want the part because you are glassing the outside of it. If you want it exact, make a mold from the plug.

Hope that helps some.