There is this news in an indian news-paper that students from other countries can come to USA in summer for work on J1 visa - dont know whether this could be applicable to all countries and for YC program as well - you may find it out by contacting USA consulate.
Please visit :
http://timesofindia.indiatimes.com/This_summer_have_a_working_vacation_in_US/articleshow/2921315.cms