Actually, if he is willing to DIY, he could build his own flow switch.
Use a piece hard metal dryer duct with a flapper at the end. Put a switch in the duct so that the flap activates it when there is no airflow. You will probably need to add a weight to the flap to get it to activate the switch. I would put a relay inline, since these types of switches are not really well suited for lots of current.
