Highlighting of not indexed text

Hello, I use Elasticsearch 7.9.3, is there any way to highlight a not indexed text, with expressions highlighted by a phrase query, and synonyms of these expressions?

As our text are often updated, if we index them, they are never synchronised with the one on web site with highlighting.

The endpoint _analyze can return a list of words for the highlighting, but the proximity between words in an expression is lost.