I like your idea, and happen to have just purchased an 11WC regulator I could use on a spare 5 gallon tank I have. The question comes in to the proper fittings to use. Ideally you would want something that just has a rubber seal like a standard regulator does where it threads into the propane tank, so that it's quick and easy to disconnect and reconnect. The one side of the regulator I believe is just 3/8" NPT. I have a four-way tee I installed the on the van and it has the same female NPT threads. Unfortunately, my knowledge of propane fittings is not great. Any idea of the type of fittings that would be required to use an external hose, and where to get them? I'm just wondering after purchasing the fittings and hose, if you wouldn't be close to the price of an extend a stay kit.  Piping in the tee that comes with the extend a stay seems to be a lot of work as new copper lines would have to be fashioned to the refrigerator and stove, and in my case to an Atwood furnace. I like your idea a whole lot better if the parts required to to the job aren't too expensive and readily available.  

Troy