I don't know what those YCers done, but I think raising enough capital to get E-2 investor visa would be the surest way now. It used to be possible to go through H1B before, but it became too tight. The actual amount of money you need to raise depends on each case; I've heard a rumor about something like $100K minimum, though it may also depend on the immigration lawyer to handle it. Absolute requirement is to show that you have a prospect to be big and hire lots of US citizens eventually.