I just ran out and bought a USB numpad, but, also had another idea…
https://play.google.com/store/apps/details?id=com.steppschuh.remoteinput
Will be testing shortly.
Edit: That app does not have a numpad. 
Edit 2: I can’t get HID macros to send a shift-up or down. According to the docs, it seems like it should be +{up} and +{down}.