Failover routing between sites that are advertising route to same network

We have two pairs of 91G's running 7.4.6 at two different locations. Each has a DMZ with subnet 192.168.100.0/29, and each location has a route map that allows redistribution of connected routes into OSPF. Site A is preferred and has route redistribution with a better metric. This works fine, but the problem is if the server at Site A goes down, but default the associated FortiGate doesn't know that server is down (the switch port is still up) and continues to advertise the connected route.

Is there a way to configure SLA to query the server at 192.168.100.2, and if that server is not reachable, then the FortiGate removes 192.168.100.2/29 from the OSPF process until the server is once again available?