Though I can't answer your question, I just curious why you want to bid the keywords of your competitors. If you have targetted keywords, just bid them in yahoo PPC, no matter your competitor have the same keywords or not. If you don't have, and your competitors have the keywords, bid on them is a waste of money. Am I right?
You can get an idea by viewing thier meta keywords. Right click on their webpage and click "view source." This should allow you to view thier meta info. I don't know if this is kosher or not though but I have used it for research purposes.