Thank you all so much for the wonderful ideas!!! Using a stylus does seem to be the most sensible tool choice, and why couldn't I have thought of some of these? That is what I love about being a SCS member, all of you clever and talented people here.
I am going to try using a stencil I have that has some wavy edges. A flexible ruler sounds fascinating, will have to check those out as well. Crafter's Companion looks like they may have something similar to what I was thinking, thank you so much for that lead, cat_woman!