How can I subtract one pose from another?

I would like to remove the transform information of one pose from another. This is useful because if you set one animation to be “additive” you only get to chose between the ref pose, or an animation/ frame of animation. But what if you need to be additive to a pose that you are pulling dynamically? I would like to be able to subtract one pose from another, resulting in the remainder as an offset to the default bind pose. This would allow me to apply this pose additively on the fly with only the pose difference.

It seems like the “make dynamic additive” node is supposed to accomplish this but it doesn’t seem to work. When I hover the mouse over it, it says “Additive pose - base pose” which I take to mean returns the resulting pose, which if fed the current pose, and the pose you want to add, will return the change in pose. Does anyone know how to properly use this?

In my poses I’ve set the additive animation type to be “local space”.