If you're in a pinch for time, you can get pretty good results just making a sprite in photoshop. Generate "clouds" in photoshop then put a radial gradient on top of it so the edges of the image fade to black. Apply this to the alpha channel and then make the color solid grey. Save it out, and now in maya you can get this to look really natural if on creation you randomize the rotation, and have the scale be both randomized and growing with particle age.
I know not quite what you were asking for, but I hope it helps,
J