How can I add stage based variables in my jenkins multibranch pipeline

I want to use enviornment variables per stage (dev, acc, prod). Now I have added this list above my pipeline:

variables: [
a : [
dev: b
acc: c
prod: d

and in my pipeline I added:

VAR = variables.get(‘a’).get(env.STAGE)

I really want to get rid of the variables list above my pipeline, but I still want to be able to get a different variable for dev than for acc for example. Any help is welcome.

I tried looking for plugins that solved this issue for me, but I couldn’t find any.