Well, when you record the rail, be sure to record it and change the DefaultCB label to your scan function. Also uncheck the index box (or else you get that indexed for each label). The only problem I don't see, is to default to the "Move+Callback" for each waypoint. That's an easy fix, and I'll post that today.
When I wrote this, I didn't envision the same callback being run each time. However, that certain is a possibility.
Check back soon and I'll have the appropriate update.
Interested in seeing your script this is based off of, I haven't even written a project using this mode yet. I just scripted it since it seemed like a good idea.
For my tamer, I use this rail engine, but in server mode.