I don't think Danny had many options, which is why it ended up being such a rich contract. Danny knew that he needed to replace Ray Allen (Ray was never coming back), so he had to make an aggressive push for JET, so the MLE was gone (once KG came back, any thoughts of cap space went out the window). If you look at the roster for pieces you might use in a S&T to get a SF back.... there isn't much, either in talent or in dollars (if you assume AB, Rondo, and Pierce are staying). It's JJJ, basically, Sean Williams' non-guaranteed contract, and not much else; hard to make the dollars work if you're trying to trade for someone making ~$6M.
They couldn't use Bass in a dual S&T because we need him.
And, they NEEDED a young SF to absorb some of Pierce's minutes, ideally someone who could give depth at the 4.
So, I don't see how Danny had many options other than to essentially acquiesce to Green's contract demands. If it wasn't Green, it was going to be scrambling for retreads like Rashard Lewis or T-Mac; as much as I think Green's overpaid, I also think there's a major dropoff between what he brings to the club versus the guys we could get on vet-min deals or with the BAE.