You should have a look at 'alive trees 3d' from Terminal 26. I think they're using the same method for making the trees in their demo.
If their thingy will cost something then maybe you could provide a free alternative.

A user called Gafgar had started writing a similar script in late 2005. I dont know what has happended to it though (here is the thread).

You could try to randomize the sprites' roll once the game starts, to make the pattern repitition of the textures less noticeable!