Then it occurred, put a simple grid on my trackpad and use BBT to map the keys to locations on the trackpad.
BTT has mapped corners and edges for input; why not the entire trackpad and allow the trackpad to be 'gridded up' with different sized grids and assign each location a single or double-tap gesture?
This would allow not only a keypad overlay but also all kinds of interesting configurations.
Archive.org still has the link for their sw download - interestingly they still host the file on the live subdomain: numapp .mobeetechnology .com
Of course I don't know what's inside it and how ancient macos you need.
I find the trackpad is so large that I do not use most of the space.
My initial preference would be to have the left side of the trackpad map to the left side of the keypad on an extended keyboard, and the right side of the trackpad to be able to be easily toggled back and forth between it as a trackpad vs a numpad.
Does not seem to be at the mobetechnology site any longer. BUT it still downloads at from the archive.org site if you search for numapp then click on the mobetechnology link.