Seasons, I have been designing in my head for some time a system exactly like what you are taking about. If you have a 2 story house, with a 2 story chimney you could run 4" pipe starting some where along the bench, bring them in from the front of the bench to draw max air flow, and cobb the whole way up the chimney to increase the mass. Run the 4" pipes up the chimney mass and into the 2nd story. At that point you have the heat where you want it and you could run those duct pipes along a floor joist to any room up stairs that you wanted. You could also run them up the chimney to the ceiling joist and take it across the house to any room down stairs where you needed more heat. I understand that you are dumping the heat up along the ceiling, and heat rises, but you are adding heat to an otherwise cold room. A small fan in each pipe powered by one of Matts units would be a plus, but I think you could get a lot of heat just gravity flow. I think you could use at least 4 pipes along the chimney, more than that and I think you might be robbing too much heat from the chimney and effect the draft. The pipes could be run on top of the bench, along the sides of the bench, anywhere you want really. The idea is similar to running water lines through the bench to steal heat for heating water. Being a Dummy, and having never built a RMH I am SURE it will work.
I have found that stupid people are always sure it will work until they try it .
Never doubt that a small group of dedicated people can change the world, indeed it is the only thing that ever has.