I got the idea from this guy-
https://www.youtube.com/watch?v=n5ecxh8DZW4
The paint holder starts at 1:10. The basic concept is a fixed base, and a top that slides along a linear slot and tightens with a wing nut. I like his ideas of having a hole in that top piece for pointed bottles, and using a secondary velcro wrap for safety.
The main difference in my design is that I'm attaching his main plate to a jigsaw blade so it fits in the jigsaw perfectly.
I see a lot of people online using small commercial clamps as a paint holder-
https://www.walmart.com/ip/Hyper-Tough-4-inch-Trigger-Ratcheting-Mini-Bar-Clamp-and-Spreader-Plastic/143577139
But I think that would be too heavy. I'm using 0.025" aluminum, which is like $6 at Lowes for a small sheet.