[CentOS-virt] Controlling allocation of ethernet devices and KVM

Running Centos 5.4 with KVM on a Dell R610 server and I'd like to control which of the four ethernet interfaces are used for specific tasks

My ideal configuration would be

eth0 - Host traffic only, no virtual guests. Used for guest mirroring and management. eth1 - NAT guest traffic only, no address for local machine and in some environments in the same zone as eth0 eth2/3 - Allocated to two different bridge devices which might be in separate network zones.

The configuration of eth2/3 is fairly simple, my issue is restricting any NAT traffic to a specific ethernet devices, and ideally one with no local IP.

Any ideas?

Steve