Predicate for quasi-synoyms (with upwards posting)?

SKOS does not distinguish between synonyms and quasi-synonyms resultig from "upwards posting" (as mentioned in https://www.w3.org/TR/skos-primer/#secalt). To give an example (taken from https://www.slideshare.net/accessinnovations/taxonomy-fundamentals-workshop-2013/37):

:xyz skos:prefLabel "Social class" ;
    skos:altLabel "Elite", "Middle class", "Working class" .

When in a retrievel or voculary mapping application each pref- and altLabel is used as synoym for each other, this creates nasty problems: If, e.g., the user searches for "Elite", she also gets documents with "Middle class" and "Working class".

We consider introducing some custom sub-property of skos:altLabel to differentiate the cases, like this:

:xyz skos:prefLabel "Social class" ;
    skos:altLabel "Social background" ;
    custom:altLabelNarrower "Elite", "Middle class", "Working class" .

Is anybody aware of custom specializations of skos:altLabel for quasi-synonyms we could re-use?

Any hints appreciated - cheers, Joachim