This is actually a work around because of some lack of functionality for automatic routing. A client of mine is used to automated routing, where the system will automatically route to an option of multiple locations based on how much room each location has.

How would serial number/lot number help with that? It appears you want different routes based on existing stock status, not new serial numbers. Have you setup Reordering Rules (Warehouse->Configuration->Reordering Rules) You may find a module that allows you to adjust how the procurements are handled, to choose a route based on location availability.