you can use it as stock.
pick the stock option and select digitize then pick the stl.
i use this all the time to go from op to op with realistic stock for verify.
you can also use it as stock in roughing cycles to cut out alot of air cuts.
i make a new layer and insert stl into file.
then copy it to a seperate layer and use 1 for verify stock and the other for rough cycle stock.
this is a great feature, play with it and you'll end up using it alot.