The gates on the Hamburg side are still intact, right? Why don't the Rheinlanders just deploy some jumpgate drop-off beacon on the other side, and make the intact gates unidirectional? The gates are important to start the jumps, but on arrival they are just a destination reference, or something.
Rheinland launches an operation in Bering and Hudson through the jumpholes, navigate near the former jumpgates (but outside of the wreckage area), and deploy the beacons/satellites). Soon larger RHeinland capitals can enter the systems (but not return that way, and Rheinland has some objectives to defend outside of Hamburg.
Liberty could have a forward (non dockable) outpost in the system, and that would be their defense point. Then take rp consequences from eh successful attack and defenses of each side, or something.