Hi,
You can configure two static routes with different preference to backup the static routes.
For example as the picture below:

Two S7706 connect to each other through network 10.1.1.0/24.
For the S7706 on the BD side,
ip route-static 0.0.0.0 0.0.0.0 10.135.228.1
ip route-static 0.0.0.0 0.0.0.0 10.1.1.2 preference 70
For the S7706 on the GD side,
ip route-static 0.0.0.0 0.0.0.0 10.142.213.1
ip route-static 0.0.0.0 0.0.0.0 10.1.1.1 preference 70
BTW, you can bind the BFD session to track the reachability to the BD/GD side connection, so that the static route could be removed correctly.