If you're meeting the cycler in its orbit, you're already on a free return trajectory back to Earth by definition. You need another burn if you want to stop at Mars and another burn after that to leave and get back on a trajectory to Earth. In any event, you need to bring all of that propellant one way or another through some combination of independent launches. I'm still not seeing what a rendezvous with the cycler craft is doing for an unmanned mission. Any delta-v you take from the cycler has to be put back via refueling or reboosting at some point or another.