W2003 Server & WinXP Prof Clients

I use "rundll32 printui.dll ..." within a batch file to connect to server
printers (but I do not provide username and / or password in the batch
file - every user has to type in his / her credentials when executing the
batch). This is needed for printer accounting.

PROBLEM IS:

How can I remove this Information for the current session?
I.e. I am logged in as user ALICE and every printed page is counted for
ALICE. But I want to print something with the Account "PUBLIC" (this may be
used for every user in our network). Do I have to "Log out" / "Log in" again
just to connect to the printer with another user account?

Thanks for advice
Martin