Someone suggested to me, as I was getting ready to film the new Easy Songs DVD, that we do a video solely on backup. Of course, vamping is the first step in any banjo backup and we do have a video on that. There are some difficulties inherent in teaching more advanced backup. For one thing, in order to move beyond vamping, you have to be able to hear your chord changes absolutely cold. You can't spend one second of time thinking about the changes if you're also going to be thinking about doing backup licks at the same time.
For another thing, backup, by its very nature, is improvisatory. There is no set order in which to use backup licks. It's more like there is a pool of licks and you have to be able to tell which one is the appropriate one to use in each situation, and you have to make that decision very quickly. But to teach the licks you have to teach them in the context of a song, so it's almost necessary to make up an artificial "backup break" to a specific song so the student can learn both the licks and how they are used. [This topic is sounding familiar. I think I wrote a Banjo Newsletter article on it last year.]
But, all those difficulties aside, that idea is rattling around in my head and I'll no doubt refine it throughout this year as I teach as workshops and camps, and with my live students. Chances are you'll eventualy see a backup DVD in our new releases.