Outsourcing term papers

The New York Times engaged in a quality control experiment, purchasing English literature papers from three online sources. The results are disturbing, humorous and worth some consideration.

"For $9.95 a page [a student] can obtain an 'A-grade' paper that is fashioned to order and 'completely non-plagiarized.' This last detail is important. Thanks to search engines like Google, college instructors have become adept at spotting those shop-worn, downloadable papers that circulate freely on the Web, and can even finger passages that have been ripped off from standard texts and reference works.
"A grade-conscious student these days seems to need a custom job, and to judge from the number of services on the Internet, there must be virtual mills somewhere employing armies of diligent scholars who grind away so that credit-card-equipped undergrads can enjoy more carefree time together."

My question: How might an instructor craft the kind of assignment that demands a product one can't possibly buy online (or grab from a dorm-mate)?