Ask YC: Stealing an idea

A former coworker had a great idea and had played around with it (just enought to get an idea of what it could do and some logos -- although I didn't like the name or logos). Since our initial conversation about it (I saw him doodling something one day), I've thought about it a lot and have a lot of ways to expand it/implement it already in my head).

The idea is great, not a huge moneymaker, but enough to get some residual income from it.

The only thing that is special to him is he knows someone that would help with supplying some items for the thing.

So, YC HN, do I steal the idea? I've talked to him about partnering, but he says he doesn't have time to work on it. I'd like to force his hand a bit and get an introduction to the contact and then hit the ground running... Maybe kick back some small % to him?

He's a great designer though and I'd love his help with that aspect...