I think a couple have. Someone is currently working on it I believe, and a forum member from the past "HDDP" did so on his race car buy using a "stand alone" computer. But in his case, his car was already a 6 spd. and he installed an "automatic SRT6" motor into his car. It's a little involved, but it can be done.
If you really want a 6 spd. and you currently have an automatic, I'd say the easiest way to do it is trade cars with somebody.
Good Luck