Visualize that the main shaft of a jet engine is an eight inch diameter pipe.                                                        Next, visualize this shaft is rotating around a six inch diameter stationary pipe. There could be ceramic bearings  between the engine shaft and the stationary pipe.  The shaft diameter at the front of the engine should be a bit smaller than the rear so you can slide this together. There would of course be a thrust bearing on the rear end of the engine shaft.

        The propeller shaft goes inside this smaller pipe. This shaft is driven by the three freewheeling fans in the jet exhaust, turning the propeller. Of course an engineer with too much time on his hands will also likely design a feathering  prop and fan blades as well, I imagine J> You can of course have both puller and pusher propellers on the same shaft  in this design. The pusher propeller can be coated in ceramic, or mounted on a rotating drum. For simplicity, I did not show this drum in my drawing.

         One note to the designer, you are going to have to put a manual clamp on the propeller shaft to keep the propeller from freewheeling in the wind. We don’t want it to dong someone on the head when the airplane is parked! 

          Thanks, Lewis Brackett