Failover WAN and wanting to access both modem UIs when primary gateway is active

[plm]

I've seen a number of examples of how to route traffic to a cable modem web UI when it's on a different subnet than the DHCP network it is providing, and that works fine for me.

The troube is, I have the same type of setup on my 5G failover modem, which I don't want to pass traffic across unless the cable modem circuit is down, and I'm struggling to find the right way to configure each of the interfaces so I can route traffic to the respective web UIs, but have the internet connection properly identified as up or down, and have the secondary link only pass any traffic in a failver scenario.

Does anyone have any posts, documentation, or other pointers I can look at for how to most effectively set this up?

Thanks.