Yes I've done it. You want very hot coals, not flames, and you'll need a pair of tongs.
The pipe must be dry, so can't have been smoked in the past 12-24 hours. Otherwise any moisture will turn to steam and shatter the pipe.
Lay the pipe on the coals, probably with the tongs, as the heat coming off the hardwood coals will be pretty intense. Let the ceramic in an all clay pipe start to glow, then remove with the tongs and gently set aside to air cool, thus curing the pipe of residual nicotine and tar.
As for the clay with the reed stem, they can be thicker and pigmented, so I'm not sure about getting them to glow..., but about ten minutes, and you might have to flip them over for an additional ten minutes, then remove with the tongs and allow to air cool.
BEWARE you must baby-sit the pipe as it cools, for it will look "cool" to others in the camp while it's still very hot.
Don't leave the pipe in the coals overnight, though some might say this is the procedure. If you forget you have a pipe in the ashes the following morning, OR if a different person makes up the fire the next morning, you will have a cured, broken pipe...
LD