Thanks very much for the pointers. I tried the "<Compose> <Space> <Space>" but, for some reason, that didn't work for me (although I am able to create other symbols with Compose).
Thanks to for directing me to the code, although on first inspection, I did not see the assignment for the NBSP. I will continue to investigate as I am able. In the meantime, I've found a workaround using a text expansion app that reliably inserts the NBSP when needed.
Thanks.