How to Prevent user from flipping Portal Registry Name in URL after Logon

Is there any way to prevent a user from logging in then changing the Portal Registry Name in the URL?

Currently if they do that and hit enter the registry flips to the one that was typed in. We have an Employee and a Portal Registry. We have separate URL’s for each registry for user to log on. I know we can’t stop them from modifying the registry name in the URL after logging on, but is there a way for the PeopleSoft system to recognize the flip in registries and kick the user out?