Seems like I saw a bunch of videos of that on YouTube...I can't really remember where or much else, but they made silicon molds of architectural details and ornate plaster and later built forms around the molds and filled them with wire & rebar and then concrete...
I can't find what I was looking for on YouTube, but these will give you some good ideas. Lookie around at all of the links on the right hand side of the YouTube page and see if these might be more along the lines of what you are looking for. I know that you can get a whole lot more detail with the silicon molds. They are used to replicate ornate plaster...
Making molds for a concrete fence:
http://www.youtube.com/watch?v...
