Drop box question

[sinnylong]

Hey folks, we're gearing up for a production of PUFFS, and I need to have a very long scroll (15 feet or so) unfurl from our fly space, the bottom unrolling and landing on stage. The gag is that there are hundreds of names of curses written on the scroll that the characters might face. The more comical the length, the better. Best would be if the scroll could unfurl and then, a few minutes later, the attached portion would be let go, for an actor to deal with getting the whole thing off stage. (Images of the NYC production attached, for reference.)

We have a batten available in the right location, I just need a little guidance on how best to construct the drop box mechanism for the effect. Nominal but workable electrics skills, if necessary. Thanks for any help!