You may not be looking for a get-rich-quick scheme, but what want actually is one. Anything that had the properties you describe (generates substantial amounts

You may not be looking for a get-rich-quick scheme, but what want actually is one. Anything that had the properties you describe (generates substantial amounts of income, quick, easy, low-risk, scalable) would be a scheme that quickly makes the practitioner rich. You are going to have to sacrifice on one or more of those axes in order to get something remotely realistic. For example, you can make somewhat disappointing sums of money with a two-week turnaround by doing crappy freelance jobs on oDesk. (On the other end of things, if you had a strong network, you could probably land a good job quickly, but building a network that can support you that well obviously takes time.)