I don't think it's impossible at all.

Are you looking to sell your idea and walk away, or find investors for your business?

Either way, you can get them to sign an NDA preventing them from copying your ideas.

Ideas themselves aren't that valuable. What is valuable is the time and effort you've put in behind them to ensure the idea is workable. To find and fix the bugs, and to figure out how to market and sell it. A napkin with scribbles is little more then a napkin.

I bet you can tell them the idea - enough to get them interested, and then work out a contract.

The other thing is - is your idea that easy to copy? If it is, what are you going to do on the second day of business? It will be public as soon as you start selling. Why not tell *everyone* what your idea is, and start generating hype. An ideavirus is *far* more valuable then a simple idea. You'll never get to the ideavirus stage with a secret idea.