I believe /login [1] is the way to go. From the look of your last attempt, it did accept the /login flag but didn't like the permissions. You may want to post your command and error message on the MSDN forums [2].
[1]
http://msdn2.microsoft.com/library/4...US,VS.80).aspx
[2]
http://forums.microsoft.com/MSDN/Sho...ID=22&SiteID=1