Is there a way to lower the air temp of a duct from a wood stove

Seems like a funny title, here is what I was thinking.. This is just a little side project that I am continually working on. I have a wood furnace with a couple of its own ducts that is separate from my other ductwork. I never need to run the wood furnace and other furnace at the same time. It is okay like this but I would like to duct just alittle bit of the air from the wood furnace into a couple of my ducts that go upstairs just to circulate some more air around. The hot air from the wood furnace I feel can get too hot to send into the duct that goes up through my wall. If I take one of the 6" branches from the wood furnace, is there something I can make to introduce some room temp air in to mix with the heated air before sending it into the duct going up the wall? I was trying to think if there was a way that the room air could be pulled into the air stream in the duct, similar to how a chimney pulls air into a barometric damper. I can't think of any way it could work.