Cross-train judo, then absorb it in to your san shou. Judo is a very practical way for a smaller guy to get a bigger guy to at least taste pavement/sand.
If it were a real fight, you would have hit him in the eyes/throat/temple/ear slaps/center of nose/testicles/center of knee cap/shin/sternal notch and back of the head and speed/clear mindedness/hand-eye coordination, not size, would have been important.