You could make two locations: one for masculine, one for feminine.
Some quick images, based on the written form:
age - Japanese fried tofu
ail - pint of warm ale
eau - water
ent - Ent
ier - brigadier
isme - pick an “ism” or picture self in Arabic language class: “ma ismik?” (“What is your name?”)… or “ice-milk”…
esse - finesse (fin > shark fin > shark skillfully making a soup and then diving in with fin surfacing)
ette - Smurfette
ie - Internet Explorer
ion - water ionizer
té - tea
ure - urine
When you have a word that ends in -ette, you see Smurfette, and she is in the feminine area of your memory palace. The two separate locations could separate the gender of the endings.
For the noun transformations, I might try to learn one example word from each group.
I started a writeup of what I learned from the Esperanto experiment. I’ll post that soon, but I think it helps to learn the mnemonics both directions.
The Table of Correlatives in Esperanto is regular: kiu, kio, kia, kie, kiel, kial, kiam, kiom, kies. I listen for the ending, like -e, which is the number 7 (boomerang) in my mnemonic system for sounds.
It’s a weird mnemonic (boomerangs on wallpaper > coffee shop > Amsterdam > mokum aleph > mokum > place), but the sound of the suffix triggers it. Then the “k” sound is “question”. So “kie” means “which place”, or “where”.
If I want to say something about "place, I can follow the association in the other direction. I find the suffix for “place” (place > mokum > mokum aleph > wallpaper of coffee shop in Amsterdam > boomerang > 7 > -e). Then attach a “ti”, “ki” or other prefix based on some other associations.
The French mnemonic “ie” as Internet Explorer might only work for written words and be good for things like studying for multiple choice tests, but if you want the mnemonic to work for speech comprehension, it might be better to encode the sound. I definitely haven’t perfected language mnemonics, but that has just been my experience so far.