This might help. Note: MYVAR is just arbitrary name I made up.
Dim WshShell, WshEnv
Set WshShell = WScript.CreateObject("WScript.Shell")
Set WshEnv = WshShell.Environment("SYSTEM")
To set the MYVAR variable use:
WshEnv("MYVAR") = "Any Value"
To remove the MYVAR variable use:
WshEnv.Remove "MYVAR"
If you use the SET command from the command line, you will get a list of all variables defined in the environment. If you need new ones, just make one up and change MYVAR accordingly. Any changes/additions made, only last as long as the user session.
Hope this helps.