I am working with an existing network that services approximately 1500 rural wireless clients [diagram: Customer], and it uses a single core Arista 7050T layer3 switch [diagram: Main Router] hooked up to a 2 Gbit fiber connection. There are multiple wireless backbones in place that deliver layer2 connectivity between that switch and multiple Access Points [diagram: WiFi AP] (Ubiquity Rocket 5AC units) with the backbones being mostly Ubiquity AirFiber 5X units.
Since this would be a fairly big layer2 network, there's routing that is used on the Access Points as well as the core router, where every client is assigned a static IP address and then a route is setup on the core switch via the Access Point they connect to, see diagram below:
The diagram shows a /24 subnet however there are additional ones configured in the exact same way so there was no need to show this information.
Because of wireless backbone speed limitations there's a need to offload some customers and put them on another service, so the idea was brought forward to add new fiber/cable/dsl services at certain tower sites where the Access Points are located and moving some of the customers to the new provider. This preferably would be done with minimal changes to Access Points, so keeping them in router mode.
Knowing that the Ubiquity equipment doesn't support an sort of source based routing, the clients will have to be routed via these Access Points and then we will somehow have to have certain clients use the present network and some move over to the new service. The new service will most likely have only a single available IP for our use so these clients would need to use NAT.
Looking for suggestions on how we could achieve this dual connectivity knowing the existing layout of the network.