Mark,
Funny I always thought of it as "noodling around" when I do what you've described. **G** I also use a lot of forward and reverse banjo roll patterns ala Doc, but definitely in the Henderson style. Thumb-downstroke/index-upstroke; like flatpicking but using the ole two fingered method. Chet used it a lot vs. flatpicking. Have a listen to "Chet & Doc" (1979) or the later released version of the same album called "Reflections". Marvelous album by the way, and I believe Dick and Camsco stock it.