You'll need a Windows console running as an appropriate user, this can be dealt with using a quick runas command:
runas /noprofile /user:domainname\userid cmd
pause
In the console you can then use qwinsta to query for a server's connections, for example:
C:\WINNT\system32>qwinsta /server:someServerHost0290 SESSIONNAME USERNAME ID STATE TYPE DEVICE console 0 Conn wdcon rdp-tcp 65536 Listen rdpwd rdp-tcp#59 userid2 2 Active rdpwd userid1 1 Active rdpwd
Guessing that Session 1 is up for a quick death you can then use the rwinsta command to kill the connection:C:\WINNT\system32>rwinsta /server:someServerHost0290 1
Done.