I was able to setup a keyboard replacement text mapping “&nbxp;” to a non-breaking space, which I copypasted from a Numbers spreadsheet originally created under MacOSX. Note I had to substitute “nbxp” for “nbsp” because stackexchange seems to interpret the HTML code! Probably a bug.
Here it is if you need it “ “.
[addendum: OMG I copypasted the character between the “ quotes above back into my Numbers test rig, and for all the world it looks like the nonbreaking space made it through! So if you’re trying to setup this trick on your iPad try pasting the thing between the double quotes into the replacement text field in the Settings->General->Keyboard->Text Replacement->+->Phrase field.]