I'm not sure this is possible from the server end. There is a way to tell who at any given moment is printing to the printers (example:
http://blogs.technet.com/b/heyscriptingguy/archive/2006/01/19/how-can-i-tell-which-users-are-connected-to-a-print-queue.aspx).
But I don't know of any way from the server side to tell who is mapped to what printer. Perhaps if you turned on some special auditing settings for print queues.
In my experience the easiest way to do this would be through a log on script run on their local machine. If you want to get fancy you can use the script to remap them and turn it on after you do the printer move and just have it report back the results of the remapping.
Below is a sample script that would just report to you what each user has mapped. It will create a text file in a file share each time a user logs into a machine, just change the PrintServer and OutputLocation variables in the beginning your print server and a share that users have write access to.