Info on the E1 (trader) and E2 (investor) on the US Embassy in Mexico http://www.usembassy-mexico.gov/eng/evisas_E.html

Highlights for the investor visa: - The investor must be coming to the United States solely to develop and direct the enterprise - The investment must be substantial. It must be sufficient to ensure the successful operation of the enterprise - must have the capacity to generate significantly more income than just enough to provide a living to the investor and his or her family, or it must have a significant economic impact in the United States

I'm not sure if a YC funded founder would be elegible, but seems hard