Kelly,
That's the way I do it. My first rod-build was a Winston glass kit back in the 70's, and Winston said that reaming and gluing ring by ring on the blank was best, so I started doing it that way and never changed. With the variety of glues available now that expand and fill tiny gaps, and the relatively small diameter of graphite rods, I don't see any reason why a mandrel-built grip couldn't be made to fit as well as one made on the blank, though. Carefully done, both methods should be about equal in longevity and performance. If I used a mandrel, I'd probably still want to glue the last ring and turn it on the rod, because I don't like to use cork checks and want the fit of the cork to be as perfect as possible at that spot.

I use TB III for my grips, btw, but I've tried epoxy, Gorilla glue, Silicone Bond, Weldwood, Barge, PlioBond, and a few others over the years and they all did the job. For me, TB III is the easiest to use and clean up, the least toxic, has the closest sanding characteristics to cork, and is virtually invisible if it flows into any tiny pits next to the glue lines, plus it's waterproof once cured.
-CC