Finale 25(.4.1.164) for Mac 10.11.6 El Capitan.

I'm working with a composer who is fond of the thunder sheet. He notates this with an irregular line, something like the wavy line of a trill, but irregular - wider for slower, narrower for faster, higher for louder and lower for softer. I experimented with Finale but he didn't like any of the possibilities. Until now he's been drawing the lines onto otherwise typeset pages, which defeats the purpose of typeset pages. We've also got to incorporate scans of those pages into the completely typeset pages via pdf merge. He's revising a previous piece, and I said I'd inquire here. Any ideas? Thanks.