Here are two options.
I cant see the back of your ears so I cant say which one is better. If your ears are thick and you can imagine cleaning them out of the mold (they will be completely surrounded by plaster) any turn will be tough to pick the clay out.
Odds are really good that across the top of the head and along the edge of the ears is still the best route.
Or... cut the ears off with a wire tool and mold them seperately then glue them on. Thats pretty common and it will keep your mold from weighing 100lbs. That will also give you the option of sculpting a different style of ear later and changing up the sculpt.