|I'm not sure loopback would apply here. If I remember correctly, the settings you need are all User settings in the GPO, right? So do you want the policy applied based on the user that is logging in or based on the computer they are logging in to?|
Is the following true? No matter what computer User1 logs in to, you want their desktop locked after 30 mins. of inactivity? If so, loopback processing wouldn't help.
Or, are you saying that if User 1 logs into a specific machine, then don't lock the desktop? In that case, loopback processing might be the ticket.
Either way, I think you'll need to come up with a group of user to whom you want this policy applied.