It is possible to run SQL Server Management Studio under the guise of another user account from the command line:
runas /netonly /user:domain\user c:\Program Files (x86)\Microsoft SQL Server\100\Tools\Binn\VSShell\Common7\IDE\ssms.exe
The command line will request a password which (quite rightly!) cannot be entered into the command. Successful authentication will launch an instance of SSMS 2008. Lovely.