Another way is with the .fpl iniBuilds file format and putting the flight plan in the flight plan folder of that aircraft. Some tools like the iniManager* or SimToolkitPro can export to this file format.
Using these files, allows you to create flight plans in other 3rd party flight planners and have a route conveniently loaded in the FMS, as another option. This can be combined with SimBrief.
*Why is the iniManager A310 SimBrief flight plan export option not working?