[exim] Using different transports based on From: address?

Hi there,

I'm currently using exim4 (Debian's 4.67-1 package) but I'm unable to find
a way to use different transports in my MTA based on the From: header set in
my MUA.

As I'm currently using an ISP that rewrites the From: header, I would like to
send emails sent with a given From: to that ISP but send any other emails (which
use a different From:) through either a different MTA or send it directly
without using a smarthost (to prevent them from getting rewrittent)

Is this doable with Exim v4? If so, could anyone provide any configuration
tips for this?

Thanks,

Javier