I've already answered this question, if not in this thread, then in others. You either missed it, or you didn't accept my answer. Trade him for anybody. Literally anybody. Hell, trade him for cap space.
The whole problem with the premise of bringing McLemore off the bench to develop him is that we're not going to develop him. If you think that McLemore is holding the team back from our goal of trying to make the playoffs this year, then you can't possibly believe that we're going to have time to stop along the way to develop Ben McLemore. I've already gone on record as saying that we can't start Bellinelli: it diminishes his overall role on the team, and it disrupts the bench's chemistry, to say nothing of their offense. You have to leave Bellinelli in his current sixth man role, in order to maximize his effectiveness.
So, suppose you agree with the idea that Bellinelli needs to remain the sixth man, but you're still on the ABM Train. Well, then, that means you're either starting Butler or Anderson, and that relegates McLemore from starter to towel waver. If you think that Karl is going to change McLemore's role from starter to, like, 7th or 8th man, you're kidding yourself. When McLemore gets pulled for good, he immediately goes from starter to being the fifth guard in a four-guard rotation. So, the answer to the question "Who do we trade McLemore for?" becomes "Anybody." Get pennies on the dollar, if you have to. Why anybody? Because we don't need to pay somebody $3M to be the thirteenth man. Anybody can do that. Anybody. Anybody at all.
If we bench McLemore, then we've given up on him. We're not going to develop him; we don't have time for that. Now, I'm not interested in arguing whether we should give up on him. But, if we do, the it's time to cut our losses, admit we screwed yet another draft pick, and get on with it. Scrub SGs are two a penny: we can easily find one for the league minimum to hold down the bench.