The only way to "find a way" would be to trade Schwarber (or move
Harper to OF). Like PC said, neither is happening (nor is Castellanos getting traded or reduced to a weak side platoon, not that a one-for-one swap of him for Alonso wouldn't be good).
And also, Harper is a good 1B! He's not a good OF.
I think concerns about Alonso's performance and future are also why the Mets haven't already signed him. They will have the win-win situation of getting to step up and keep a beloved player while getting a cheaper deal than he hoped to get on the open market. He turned down 7/158 last year.
Rosenthal recently said "the entire industry" believes he'll be a Met again.