I use http://lessonslearned.org/sniff . I check it reflexively every so often, as Verizon has at least once re-enabled the super cookie after I had disabled it. That site checks for cookies from other carriers as well.
I guess it could be automated in a small way too, such that if the cookie was detected as being returned to the browser then the site gets flagged and it won't get it again.
Alternatively, only add the cookie when requesting pages from partner sites known to be tracking it.