Yes absolutely. There was a hemorrhoid treatment made of activated charcoal called Freedhem that was applied rectally. It is no longer available on the market. Also, for prostatitis, Dr. Thrash, former medical examiner of the state of Georgia, used an activated charcoal enema with success.
Yes, activated Charcoal (AC) can be given rectally. Although this is a veterinary journal, I doubt the principles are different and according to this article it's given in a liquid slurry, much like oral administration:
Enemas also have been used to decrease the colonic bacterial numbers
and substrates. The following types of enemas have been recommended: