I have no idea about that particular game, but there are on occation patches made for popular games to run on a lower shader model. Bioshock comes to mind. It's a huge job though. You need to rewrite most of the shaders the game is using, in some cases it can't even be done without major quality og speed regressions (hence why the game is released as SM3 only).
You could give it a search (the game's official forum would be a good start), but I doubt you'll find anything. Buying a new middle to low end card is probably the best solution. They're dirt cheap these days, and are probably still faster than what you've got now (what is it BTW?).