Detecting Rogue VPN

I have an interesting scenario where one of the managers at the a remote site insists on running his own VPN.  Outside of flying to the remote office with a hammer and removing said VPN.  I was curious if anyone can think of a way to block anyone connected to it from traversing the corporate VPN.

The traffic flow make it a little tricky..  Internet --> Rogue VPN --> RDP to local workstation --> local workstation to Corporate LAN