As lostatsea suggests, your best solution is likely to manually build up a fractal by:
1) generating a basic shape at lower resolution,
2) resample to a larger resolution (typically 2x, but probably not more than 4x),
3) perform difference clouds as many times as you like,
4) and repeat steps 2 and 3 until you get a size that you like.

I'm really lazy and use a fractal generator program like Wilbur to do something similar to steps 2 through 4 for me automatically at the size I specify.