Ask HN: Don't want to steal an idea, but don't need 4 non-technical cofounders

Basically here's the situation: I met this guy randomly at the bank, we discussed some business ideas we were each pursuing. He has an idea which I think is great, but requires a real web app - right now he has a website built with GoDaddy's website builder tools. That's about as far as he's gotten with the idea. No users, no working product yet. I had a meeting with him where I told him that I had a ton of ideas for the business and I think I could build him the real web app he needs. I also found out more about how far he's gotten with the idea. He has 3 cofounders besides himself: 1 guy is in school for computer stuff, but not really ready for prime time yet. The other three (including the CEO who I talked to) are all undergrad business major types who work as tellers at a bank. So HN, what is the smart AND ethical play here? I have the ability to execute this idea entirely by myself. These guys have zero ability to execute - no one on their team has any exp