Is there a cudaminer difficulty parameter option
No. Difficulty is handled server-side rather than client-side.

Different pools have different policies regarding difficulty. Some pools have a fixed difficulty. Others automatically calibrate the difficulty depending on your hashrate (this is called vardiff). And some let you set the difficulty, on the pool website. But in any case, it is ultimately the stratum that sends out and accepts work, so it is the pool that dictates difficulty.