Just before I stopped full time instructing I managed to get a ground/air instructor working weekends and a solo hire machine.
The idea was that the solo hire plane was just sitting there and the instructor was there to sort out any issues with flight checks and also doing the job of selling and answering any questions. They could also jump in and give briefs to trial flights so that when the plane got back they could just jump into the cockpit with a brief word to the instructor that was taking it which routing they wanted. And if someone was late back off a nav ex we could just jump in with any available aircraft.
Worked pretty well to be honest, I usually tried to do that bit with a swap with one of the others when they wanted lunch. I was flying 20 hours plus a week anyway so having a day or two on the ground wasn't a hit to my pocket.
The instructor on the ground though needs to be a face of the company and good at selling for it to be productive.