I don't see how we'd be adding a first in the deal, because we're doing them a favor. We're taking the grossly overpaid, non-defense playing Lee off of their hands so they can sign a guy to a max contract. Lee might have some value to other teams, but he just clogs up our roster even more. Add a protected future first round pick from GS and I'd consider it.
Though, I must say that it'd be extremely interesting to put Green in that lineup. A lineup of Curry, Thompson, Iggy, Green, and Bogut would be [dang] near perfect for Green. He'd be third or even fourth fiddle, and he'd be at PF where he has an advantage. So, of course, he'd dominate as a third option. For GS, he's an upgrade at the 4 from Lee because he plays defense and can stretch the floor more. The only concern would be rebounding from Green, since he's not that great of a rebounder.