Since these aluminum ducts get quite warm when the dryer is running,
what about building a long duct/box abt 10 x 10 inches around the dryer duct?
Maybe construct the box from coroplas or even some cheap wall paneling.
Then pump air into one end of the box, and let it exhaust at the other end..?.
Kinda based on the lab condenser idea..
With the right amount of air flow, you should be able to keep some of those BTUh indoors.
Efficiency might not be that great, but it should be able to pay for the power it uses.
A few
free BTUhs are better than zero BTUhs.