Just to throw this out here....
The cubs could in theory send Schwarber to AAA to get him split time duty catching with Contreras a la their AA time. It wouldn't be popular with fans for obvious reasons but I think you'd get buy in from Schwarber's camp because he genuinely seems to want to catch. AAA still has the DH so both still hit every day but if you're really on board with him being a C this seems like the best case to get him ready fast.
I obviously get why people would be suspect of the idea. But the thing is, their offense with Fowler being added is still really fricken good. So, it becomes more a question of do you believe in him as a C. Additionally, he makes for good insurance if Soler gets hurt/is ineffective and you give both every day playing time this way.