[exim] smtp_load_reserve and priority ips

I have this in exim.conf.

deliver_queue_load_max = 3.0
smtp_load_reserve = 15.0

When the load on exim gets real high I guess whats called load reserver to
kicks in. But I also have this is exim.conf.

hostlist relay_hosts = net-lsearch;/etc/virtual/pophosts :
/etc/virtual/relay_ips : 127.0.0.1

Relay_ips contains the Ip pools we own and want to relay for no matter what.
Pophosts contains a dynamic list of IP's that have pop'ed email in the last
15 minutes. Is there a way to have exim only refuse messages from clients
not in these lists when load gets high?

Thanks.

Matthew