Trumbull,
I hear you! In fact, as I understand it, you may use upper-cell numbers in a Nemeth numeric key.
The Guidance says that we may not use UEB symbols within Nemeth Code context, but upper-cell numbers within a Nemeth numeric key are in fact Nemeth Code symbols from the Nemeth Code even though they have the same dot configurations as UEB numbers.
So, make sure your key listing is clear, including, as always, using the same symbol in your key listing and in the graphic/table, and you should be good to go.
Sense make?
–Kyle