I was gonna say you could put the rubber band next to the base of the bottles, then I realized the syringe things wouldn't be able to go in, so maybe put it directly on the bottles instead? but idk if that would work because since it's a rubber band, it might just always be squeezing them together.
but that won't work since the syringe plunger things (idk what to call them) would move with the lil square, so pulling the bow back wouldn't change anything about the rubber band. You'd have to put it directly on the bottles.
I do have an idea with just a regular string, but idk if that would fit with the aesthetic you're going for. It's pretty similar to what you already have with the rubber bands so I won't bother drawing a diagram and stuff.
you know, this would probably be a good idea for its own thread. I'll try not to derail this one.
as for what you should actually do, I legitimately have no idea. If I had to say something I'd say put the rubber band on the bottles themselves.