I'm sure Lewin could handle a corner outfield spot, he's a very solid defender. But as it is, Cooper can hardly play the outfield. Lewin would probably be a defensive upgrade in the outfield, if we're being honest.
That takes care of the roster spot but it doesn't solve the problem. Neither Aggy nor Lewin can play the OF. Which means that you can't ever have Aggy and Lewin together in the lineup. That means taking away ABs from Aggy.
I think that the best thing to do is to bring up Sanchez and send Cooper down. Have Dickerson, Brinson and Sanchez in the OF with Duvall on the bench to see how that goes. At least until Marte can return.