We have exactly the same situation here. The (direct) object of ghoS is the path followed, not the person following it, so since the prefix qa- indicates a person, it must be indicating the indirect object. There's your prefix trick right there. DujDaq qaghoSmoH means In the ship, I cause you to go (along some unspecified path). It's ambiguous in the sentence whether you or I or both of us are in the ship, but you're not going to the ship. Going to the ship would be Duj qaghoSmoH or SoHvaD Duj vIghoSmoH.