[Exim] another auth question

Is it possible for an AUTH attempt to be handled by multiple
authenticators? It seemed logical to me that if I set up two
authenticators of type PLAIN, PLAIN attempts would be tried first against
the first and then against the second. This seems to not be the way it
works. Because I have two very distinct user types I have to support, it
seemed to make more sense to have two different authenticators, one that
knows how to authenticate in one way, one for the other group. In
addition to being a _much_ simpler config, I like the fact that the logs
would easily tell me which class the user was in (in the A= part).

here's an example of what I tried to do:

system_users:
driver = plaintext
public_name = PLAIN
server_condition = <lookup in system db>
server_set_id = $2

special_users:
driver = plaintext
public_name = PLAIN
server_condition = <lookup in special file>
server_set_id = $2

only more complicated =). I was expecting that if system_users returned
"no", that then special_users would be tried.

Does what I'm talking about make sense, and does the ability to do it
exist and I just missed it?

Thanks
--John