Nagios check dependent on second nagios server

We have a dual Nagios server setup. One is setup for internal server monitoring on our LAN, while the second Nagios server is hosted externally and is used for external checks only such as URL and ping checks form the WAN side.

I was wondering if there is any way to setup cross dependencies between the 2 servers so if an internal alert for apache down goes off. Our external Nagios server does not start alerting for websites being down.

I suppose each could check for the other being up. It is a bit hard to launch them so simultneously that neither complains, but it should settle down pretty quickly.