I’m flying the wonderful Just Flight Bae146, and achieve the multi segment flight as follows:
Plan the original leg in Simbrief, say EGLL to EGCC. Load into the MSFS world map and place rhe aircraft at EGLL. Load the flight plan and aircraft weight and fuel into the 146 EFB and FMC directly from Simbrief. Fly the first route to EGCC, using ATC if you wish. Park at EGCC and refile EGCC to EGPE in Simbrief and generate the plan. Now reload the flight plan from Simbrief into the EFB and FMC, and the EGCC to EGPE flight route will load. Then use the EFB aircraft page to load the new pax and fuel figures into the aircraft. I haven’t found a way to load the flight plan into the ATC system yet for the second and subsequent legs, so I’m ditching ATC at present.
I’m currently using this system to simulate diversions. I fly the original plan to destination, the 146 FMC route system includes the go around procedure, so into the hold after the missed approach. While in the hold I edit the Simbrief flight plan to go from original destination to alternate airfield, with no additional alternate. Back to the aircraft, reload the flight plan into the EFB, without changing the weights in the aircraft section, so no change of fuel load. Reload the flight plan to alternate in the FMC and route direct to the first en route reporting point. I’ve used the same technique in the FBW A320. Enjoy.