from cam_mod.ini

; FM selection can also be done with command-line options (which override mod.ini)
;   -fm        : to start the FM Selector
;   -fm=name   : to start game with 'name' as active FM

Create a shortcut to ss2.exe and add -fm=<the folder name of the FM in the FMs folder> to the path

so for example:

"C:\Games\System Shock 2\ss2.exe" -fm=PonterbeeStationV5-ND