Sculpting chocolate, Mermaids, HELP!

Hello fellow creative types. I would very much appreciate it if someone could help me with my dilemma. I have been asked to make a chocolate mermaid to sit atop a chocolate wedding cake (choccywoccydoodah style). I have in the past used chocolate plastique to make roses etc so know that this wouldn't be the right medium. I have used the method of blitzing chocolate down in a food processor until pliable that is mentioned in Jean-Pierre Wybauws Chocolate Decorations book. I found this tremendous for making banners etc but you don't get a great amount of time to play before it hardens, also your working with small quantities. Does anyone know please what I have to use to sculpt a larger piece., I have been searching for well over a month now and can't seem to find the answer. Thank you