I'm fairly sure you can sue him and get him to pay the 15% for the Social Security tax.

You might be interested in this article:

http://www.inc.com/guides/managing-independent-contractors.h...

This article is actually aimed at the employers, but it warns them about the IRS re-classifying contractors as employees.

Some interesting bits:

"Legally, the contract is a key part of establishing a non-employee relationship, though it doesn't guarantee that the IRS or other agencies will agree that your contractor should not be reclassified as an employee. If the IRS deems an employee misclassified as a contractor, some states – particularly Colorado and Maryland – can enforce hefty tax penalties on the employer. When in doubt, consult the IRS's guidelines on the difference between an independent contractor and an employee here.

With the IRS estimating that 15 percent of the U.S. workforce is misclassified, you'll want to be firmly within legal grounds – and to document a work arrangement meticulously – when working with an independent contractor, so that there is no doubt about the nature of the relationship.

The basic rule, experts say, is that you determine the what and the contractor determines the how. You say you want a piece of market research or a graphic design turned into you by a certain date; the contractor decides how to create these deliverables, subject to your approval. It's important to outline specific goals, but the contractor must provide their own tools, equipment, and facilities to complete the work.

In probing the nature of the relationship, the IRS might examine the contractor's level of freedom, including setting his or her own hours, paying his or her own business expenses, and hiring support staff or assistants as necessary."