How to prevent iTunes from trashing older versions of apps on updates?
I solved this by setting up a folder action using Hazel to automatically move any file in the trash with the extension .ipa or which is otherwise recognized by the system as a Mobile App to my iTunes/Mobile Applications folder. I'm sure you could set this up without using Hazel, just using folder actions. You will need to make invisible files visible before setting the action so you can at Trash as location A.