Scripting a registry change for all users on a Citrix Xenapp 6 server

Hello,
I have a misbehaving application that the vendor says requires a registry change to fix.  The application is published on a three server Citrix Xenapp6 farm and this registry change must be applied to each user who launches this application.  They have provided a .reg file that can be executed to create the appropriate keys but to accomplish this without a script we would need to log into the desktop of each Xenapp sever and execute this .reg file.  I need a method to script this registry change/addition when ever anyone logs into this server or this application.  For example, user one launches the application and is directed to Xenapp server three.  This Xenapp server should have a script that adds this registry key at logon.  We are using Termlogin.cmd to run various commands such as mapping drives, etc but I need to know how to execute this .reg file.  Any help would be greatly appreciated.  

Thanks.