[exim] Strange authentication

Hello.

I want to do the following: I want to set authentication depending on the
MAIL FROM command.

For example:
MAIL FROM: a,b,c
should do the same as:
USER a
PASS b
MAIL FROM: c

The idea is to use authentication with clients that cannot do smtp auth (a
motorola v3xx cell phone in my case).

Can this be done?
Can I set sender and authenticated_id somehow?

And no, I do not want to use SMTP after POP.
And yes, everything is SSL-encrypted already.

Regards,
Steffen