Thanks for the response. Unfortunately using Autohotkey isn’t a helpful workaround.
Steam will let you create custom controller configurations for seeming any app opened through Steam.
I did some more research last night and it seems like Steam controller configurations don’t work for the same reason the Steam overlay doesn’t work. I don’t understand what that reason is, but it sounds like it’s something the developer would need to figure out.
I’m trying to use Aseprite on a tablet. I can map all of my commonly used hotkeys to a controller that I can keep in one hand while drawing with the other.