Target Lg noun subclass with its own form of a suffix

Question

In the source language Mato, Proper Nouns take an associative suffix -am in the same way any other noun does:

However, in the target language Uma where the normal Associative suffix is -an, Proper Nouns seem to take their own form of the suffix that does not follow phonological rules, but is assigned according to its subclass:

Yesu Nasaret-gano (*Yesu Nasaret-ian) "Jesus of Nazareth"
Josep Erimatea-nggano (*Josep Erimetea-n) "Joseph of Arimathea"

With limited data, it appears the Associative suffix for proper nouns is -gano / [C]_ and -nggano / [V]_

How do I handle this in the FLExTrans process? My inclination is to create a target lg template for the Noun subclass Proper Noun and populate it with the ASS5 suffix -gano (which would be a separate entry in the lexicon, not a separate sense since I have no way to distinguish the suffix's form in the Allomorph section), then write a choose statement rule under the Noun rules that if its a Proper Noun and the Associative slot contains "ASS", then set it to "ASS5".

Will this work? Is there a different way to approach this?