When it is freezing, I wrap Christmas lights around the feeders, making sure no light blocks a port. It works, the lights (usually red ones) are pretty, and the hummers can warm up to them too.
I also add a feeder up under an eve near an outdoor light--again I use incandent lights for the added warmth. The eve traps some of the heat, and it is out of the wind.

Christine Southwick
N Seattle/ Shoreline
clsouthwick at q.com