How can I create a virtual subnet that spans multiple servers?

I have some CentOS 7 servers hosting VMs. The VMs are connected to a network bridge on their respective hosts that allows them to communicate with each other and with the host (via a dummy adapter on the host). The hosts also each have a physical adapter which allows external communication. **The bridges must not be connected to the physical adapters.** This diagram should make the current layout clear. Subnet A connects the hosts to each other. Subnet B exists entirely within host 1. Subnet C exists entirely within host 2. **The VMs must not have addresses on subnet A.** I'd like to combine the two bridges into a single virtual subnet so all the VMs share the same address space and broadcast domain. Is there a way to do this? Here's the goal: The VMs have CloudStack "public" IP addresses, which need to belong to their respective subnets. The VMs must not be in the same address space as subnet A. CloudStack public IP ranges are defined at the zone level, so the VMs would have to be all on the same subnet to get them into the same zone, let alone the same pod. The hosts can route traffic between the subnets. I can't add more subnet A addresses to the hosts, and I also can't use NAT on the hosts. I'm also unable to set up VLANs in subnet A. For most purposes, subnet A is outside the scope of what I can control.