How could I create an Analog Density Knob?

Hi gang, wondering if we can brainstorm on this or if anybody already knows of a solution on Soundflow or somewhere else. I'm using my tape machine quite a bit but don't care for touching the gain knobs on them as they can sometimes have issues. As a solution I have been adding the external insert in between two trim plugins with inverted values. I think it would save quite a bit of time to have these trims affect each other, for example if I increased the first by 5 db, the second trim knob would compensate -5db automatically. It could be a quick way to find a sweet spot with driving the machine.
I'd love to find a simple Soundflow-safe solution that uses the 3 native inserts I mentioned (trim, insert (external), trim) and I can't quite figure out how I would do this.
I'm also curious if anybody knows of a third party option that does this for you all in one plugin - I'd buy it.