I don't see a way to employ external commands in the process of picking highlight using existing means (and not sure I get how it would work, probably like some kind of predicate that gets path to the file).
However, in principle you can highlight file by full path like this:
highlight {{/home/user/some/file}} ctermfg=red
I say "in principle", because the pattern is accepted, but doesn't work (pattern is matched against file name only, which is a bug). So thanks for implicit bug report :-).
By the way, you might not be satisfied with performance of running external application to determine file highlighting. Even with obviously employed caching the slowdown might be noticeable.