I bought a set of brake spoilers from a Porsche GT3. They are plastic and are meant to snap to the control arm. They are relatively cheap as well (~$30). I didn't get a chance to fit them yet, as they will require some trimming. I think they work better attached to the tension rod, but seem to fit nicely on the wishbone. Both methods will require zip-ties to secure, but shouldn't affect turning the wheels. This seems like an easy way to get some more air-flow to the brakes without a hardcore duct that may be limiting on the street. Hopefully I'll get a chance to try it out.
(Pictures borrowed from suncoastparts.com and blogspot.com)