Dred,
I do that with my 3rd finger. I just copied it over from banjo. You can play the melody and runs with the thumb, then brush down with the 3rd finger, then pluck up on the first string with the 1st finger for an effect like hitting a banjos fifth string. So the guitar's first string becomes a drone string, but you can fret it (which you rarely do on a banjo).
So the basic strum (or roll) is the same rhythm as frailing, but frailing starts the roll with the 1st finger. But here you do the frail roll in reverse. So here you would thumb for a half note, brush down with the 3rd for a quarter note, and then pluck up on the first string with the 1st finger for a quarter note. Later you can hit a series of notes with the thumb instead of the brush-and-drone sequence.
You can put a pick on backwards on your 3rd finger, but I found it awkward.
Thank you for letting me sound like I know what I'm doing.