[exim] Rotating SMTP Outgoing IP addresses

I've ashed this before and I don't think I got an answer. Does anyone
know a good way to set up exim to send outgoing mail on a
rotating/random set of IP addresses? The idea being to get around per IP
rate limiting on the other end. If no one has done this I can probably
eventually figure it out but why reinvent the wheel.

Thanks in advance.