I think part of how we get past these culturally conditioned preferences is by changing our approach to dating. The way most people do it now, which involves going out with strangers chosen for attractiveness, gives us little opportunity to discover how attractive someone different might become if we gave them a chance.
There is a better way. People are far more open-minded in choosing friends, and most of us have diverse social circles. If we chose dating partners from among our friends, people we already like and trust, we could get over "types" and start to appreciate other kinds of beauty.