The most clever, if unsavory, way that I've seen someone solve this is by building a free adult website and requiring users to solve captchas to view the content.
Once they had a regular stream of people solving captchas, they started selling the ability to insert the captcha you need solved in the visitor stream.
Once they had a regular stream of people solving captchas, they started selling the ability to insert the captcha you need solved in the visitor stream.