Can you use:
- the WCONN... Functions in win32api.
- SUBST
- NET USE

Example:

DECLARE INTEGER WNetCancelConnection IN Win32API STRING, INTEGER
IF WNetCancelConnection(cDriveLetter, 1) != 0	
&& 1: disconnect by force even if any file open
nDType = 3									&& if fail to disconnect because the folder was *Substed*
ENDIF

IF nDType = 3			&& local hard disks, including *Substed* drives
	cMapCmd = "subst /d " + cDriveLetter + " > nul"
	RUN &cMapCmd
ENDIF

IF cDriveType = "NET"
	cMapCmd = "net use " + cDriveLetter + " " + cDrivePath + " > nul"
ELSE			&& regarded as "Local", do a subst instead
        cMapCmd = "subst " + cDriveLetter + " " + cDrivePath + " > nul"
ENDIF
RUN &cMapCmd

Cheers!