The room where I sew does not get any airflow through the one register in the room. Two different heating/cooling companies could not determine why. My husband found online for about $60 a register cover that incorporates two small fans which literally suck air up through the duct and into the room. It has a small on/off switch on the register cover, which I turn to "on" when I'm in the room working, and I turn it off when the room isn't being used. It plugs in to a nearby wall receptacle. Works like a charm and impact on the utility bill is undetectable. Google Airflow Industries.
Maybe this would work for you.