I take it that they are essentially installing a pre-hung door unit sized to fit within the existing jamb....? If so, and filling is not acceptable, perhaps the door stops could be removed, the temporary jamb screwed into the area behind the stops, and the stops replaced after the door is reinstalled. That way the new holes would be concealed by the stops.
Alternatively, I'd think it wouldn't be hard to secure the temporary door from the inside with the frame up against the existing stops with screws into the jambs in the area covered by the door when it's closed. Filling there wouldn't be noticeable.
Screwed on after refinishing.