There are automatic USB switches out there, but they can be absolute monsters when they want to, especially anything with bidirection communications -- Usually don't work properly or causes havoc. And whatever you do, DON'T send two jobs at once. LOL.
As mentioned above, just get a third cheap system that can run the software properly, and then either set it up to recieve remote print jobs (Print networking/whatever), or set it up to use Remote Desktop.