So the answer in my mind is "of course pilots can fly circling approaches at non-towered airports" (seriously, I could swear that I've done it before, but then again I can't think of any specific examples....).
That is, until I ran across this little tidbit in the Air Traffic Control Order while researching another question:
a. Circling approach instructions may only be given for aircraft landing at airports with operational control towers.
So then the question becomes, why do they have circling minimums at non-towered airports??
- No tower here.
- ATC can't clear me to circle.
- Why do we have circling minimums??