As a committed number pad user for years, the solution you've used (and that I have used) has done away with my need for a discreet number pad altogether. I have one layer that turns the right side into a number pad, and another layer that turns it into a VIM cursor control pad. After all these years of typing on an Ergodox in this way and dreaming of a separate number pad, it turns out I had what I wanted all along and can't leave it now.