I have a portable tank with a "Y" and 2 shut off valves. These feed 2 hoses that have a connector on the end just like the portable tanks. This allows me to run my portable grill, stove, lantern, and heater from the portable tank. I can run 2 appliances at a time; 1 from each hose. I've been using the same set up for about 20 years with no problems.
I think the hoses and "1 pound tank fittings" came from Mr. Heater. I got the "Y" fitting and valves at a welding gas supply place.
I would think the same thing could be done to the tanks on the RV. Just put a "T" into the line between your tank and regulator. Add a shut off valve, hose, and the fitting on the end to match the throw-away tanks.