Bend node that acheives layered blend by bone activated by bool

Hi!
I have a FPS character most of the way set up with movement, but I’m having a small issue. I am using procedural aim offsets, which works well, but I also want cover lean animations for Q and E. I have attempted to set this up with an additive blend space and a layer poses by bone at the lower spine. Unfortunately, this has the effect of adding extra sway to my weapon and side to side movement while running.
I tried using blend poses by bool, but then I have to create lean poses and animations for every place a character might lean, so back to the layer blend poses.

What I would really like to achieve is the functionality of both. I would like to blend layered poses by bool by bone. That way I can turn the layer off when not leaning and only activate it when leaning.
Is there a way to achieve this?

Thanks in advance.