Here is a suggestion. Why not follow the "British Masters" policy, and simply give titles names? "British Masters" is a title, and give boxers something to fight for, but in itself it is not claiming the holder is "champion" of anywhere.
We are seeing "challengers" for the British title , Commonwealth title etc that are in no way, shape or form, legitimate contendors for the title of "Champion of the..."
Also we see intrim world chapions, superworld chapions, from several bodies. At no point is this title really claiming the individual is the champion of the world.
And don't get started on "international...." title.
But yeah. The British title already has a name "Lonsdale Belt." Why not simply say "The two fighters are contesting the Lonsdale belt, without the facetious claim that the winner is the champion of Britain."
Commonwealth could be the "Rainbow coloured belt," WBC International titles could be "the black piece of pastic-leather with a metal badge on it," area champions could perhaps be given a trophey like they do with amateur boxers.
But yeah- its a bit like the prizefighter concept- an award, something to aim for, but without the generally meaningless claim of being a regional/national/global champion.