How do I structure an Independent Contractor Agreement for an incubator?

My friend is starting an incubator and wants me to contribute ideas for new mobile apps. He sent me an independent contractor agreement, but I'm concerned about who owns what. We both agree that there should be some co-ownership of the new apps that are incubated. However, the appropriate splits are hard to determine in advance, especially since we don't know how much I'll actually contribute to each of these new apps. He wants me to sign an Independent Contractor Agreement, but it contains a bunch of clauses that state that anything I contribute in the performance of my contract, he owns. Is there a way to craft this ICA so that if I give him some of my ideas for apps, he doesn't just own them outright? I was thinking of just modifying the standard ICA so that instead of granting him ownership, it grants him an irrevocable, non-exclusive license to anything I contribute. And that if we get serious about these ideas, and I get involved, that then we'd negotiate, on a per-app basis, what the splits should be. (And I'd confer exclusivity at that point).