Well, I don't see alot of options for this one really... You best shot is wiring the "main trunk" back up with some curve in it, and letting the right branch be your cascade... I would look to remove the left branch altogether... Either way, it will take time, procumbens don't grow very fast and you can pick them up here in Atlanta for $5 bucks a piece... A big one would set you back $20...
All that said I would search the forum and gallery for cascade bonsai, look at a lot of pictures to really help you learn the technique of styling. Looking at photos is the best way to learn, especially if you really study everything like movement, branching, pot selection, etc... I would, of course, reccommend you get some books. You can check your local library for free information. I would reccommend Harry Tomlinson's book. I can't remember the name but it is something generic like "complete book of Bonsai" or something like that and about $30 new. It is a great learning book with nice pictures and help on most speices. John Naka's books Bonsai Techniques I and II are invaluable books, kind of the bonsai unofficial bible(s)... They are pricey though, about 40 a piece, but worth it. You can get them here:
http://www.bonsaimonk.com
Hope that helps some...