You don't need to install the shifters anywhere, as long as the initial stretch of the cable (from shifter to the first frame boss) is covered by cable housing. All you need to do to make a representative test is to install a piece of housing from the shifter to the frame (can be shorter than usual), and then route the cable all the way to the derailleur(s) the usual way. Whether the shifter itself is installed somewhere or hangs freely has no impact on its operation.