Leslie,
You might try casting the butterfly or other objects in acrylic, using a slightly modified version of the technique described in the "Articles" section of the main Penturners site. Just stick with clear (unless you want it colored) acrylic. You might want to do it as a 2-part pour, as described by Anthony (Penworks) in a recent thread. Basically, pour a small amount of the acrylic and let it begin to set, then put the charm or other item on top, then pour an additional layer of acrylic. Waiting for the first layer to set up should help the charm stay suspended, and the two layers together should come out without much of a line (if any) if I understand Anthony's results correctly.
You might not want to use the soap molds, though, unless you also use a release agent inside the mold (it may work, but I'd hate for you to ruin a mold; I'm not sure how expensive they are). Good luck, and please post your results! (of course, post 'em in the Casual Converstion section...yes, that's an inside joke)