How to logout users from a windows service without knowing their name and password.

Question

I've been beating my head against the wall over this, and am only able to find very little information pertaining to my problem.  I am writing a service in Visual Basic .net that will monitor an internet connection.  If the internet connection goes down I want it to logoff any user currently logged on.  My problem is this.  I have found out how to logoff the current user with the ExitWindowsEx API.  And from reading I think that the secret to logging off another user on the system is by impersonating that user and then running the ExitWindowsEx API call under that user context.  However, I can not figure out how to impersonate a user (as an administrator) without using the LogonUser API that requires a name and password.  How do I obtain user tokens for users that are currently logged in, or any user for that matter, without a name and password if I have administrator rights?

I know there has got to be a way to log out a user programmatically from a program or service that is running under the context of the administrator, or system, etc... Please help.