Well it's quite a long script, but this is the part what it's all about:

BREAK OFF (-> this is on top of the script)

IF @WKSTA = "PDKCITRIX1" OR @WKSTA = "PDKCITRIX2"
IF @INWIN = 1
; WNT
;SHELL "\\pdkfp\netlogon\logout.bat"
ENDIF
ENDIF

and the logout.bat contains the following:

IF %COMPUTERNAME%==PDKCITRIX1 GOTO LOGOFF
IF %COMPUTERNAME%==PDKCITRIX2 GOTO ENDLOGOFF
GOTO ENDLOGOFF
:LOGOFF
For /F "Tokens=1" %%I in ('\\pdkfp\netlogon\queryuser.bat') Do Set sessions=%%I
IF %sessions%==1 goto ENDLOGOFF
msg %sessionname% U ben al een keer aangemeld en wordt uitgelogt, neem contact op met afdeling ICT
sleep 3
logoff %SESSIONNAME%
:ENDLOGOFF

Hope you can do something with it?