Passing varibles from xp workstation to win2003 RDP session

I need to setup individual user accounts for each of our employees. Currently I am using generic accounts to run only a specific application through RDP and I have to have a user# variable set so the program knows where it is running. I would like to be able to set that variable on the workstation instead of the session on the server and have the server pick it up from the workstaion when the user connects. This will allow my roaming users to have their own accounts and the software to know where they are located when they connnect.