Android S.Pen button mapping (to undo specificially)

I would really appreciate you guys adding the ability to map stylus button to undo. in the past few years nearly every other art program I use has added this functionality... besides previewing brush sizes with hover (which I know is difficult to implement and only a few other programs have it) this is the second most useful and workflow improving feature I can think of, having to constantly hold my finger over undo while i draw with stylus feels like it slows me down a lot.