[EXIM] gecos (fuzzy) matching with exim?

I'm searching for a possibility to match the gecos field from /etc/passwd
with the userid when receiving mail (like sendmails MatchGECOS option).
As I understand it, lsearch works only the other way round (from userid to
full Name).
I think I heard that "it should be possible", but did not found a hint
in the documentation.

Many Thanks,
    Thies

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Thies Lehmann                Information Systems - Faculty of Economics
                                                    Freiburg University

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