Here is a link to some information on silicone products. I personally have never tried so can’t comment like others. Having said all of that the research says that some types of silicone (as on this link) do a fine job of fitting until cured, then releasing once set properly. I have plans for the same methods in the future simply because I am troubled by not being able to find some specific characters from the time period I am after.
http://www.bare-metal.com/polytek-mold-materials.html
There are also some good articles on modifying figures on these boards, so over time, a mold could be made to recreate several at one time in a single mold. Let us know how it works out if you go this route.