[Exim] gecos as user alias

Assuming the gecos field is always the same format
which is usually "name surename" - is there any way
of using this information as alias?

Right now we have a realnames alias file looking like this:

name.surename account
name.surename account
name.surename account
...

So the aliasfile director can easily lookup the
name/account. But this is not longer suitable since
soon our users come from a LDAP server.

My thougts:
If the local_part includes a "." we could do a LDAP
lookup of "name surename" and on success return the
account. The result could be used in a smarthost
director to set a new_address to the account.

Since these are my first LDAP tries with exim
can someone please comment on this... :)
--
Torsten