[exim] Rate Limit Message Relaying

Can this be done?

I'd like Exim to be able to rate limit outgoing messages from certian IP
addresses who I would otherwise relay for. Initially I'd like to
restrice the rate to one message per 30 seconds and after 5 messages
climb to 1 message every 2 minutes - or something like that. Is this
doable? Sort of like the bounce retry stuff but applied to relating
instead of retry.