How does the recent income immigration rule for spouses apply to a self employed person?

In the U.K. you now need to show you earn over £18,600 to be allowed to bring your spouse (married partner) into the U.K. from a non EU country. Does anyone know how the new income rule works if you are self employed? As you may know, a self employed person can claim numerous costs against tax as they run their own business, such as their car (used for work), office in the home, phone bills, clothes, etc - this reduces the tax bill, but it also reduces the income stated on their books. In other words, a self employed person may show an income of, say, £15,000 p.a. after business running costs of £20,000, but this equates to an employed person earning £35,000 p.a.

Would the self employed person be able to claim their gross income was enough to support their spouse, or does the rule apply to their net income?

One solution might be to set up a limited company, and pay oneself just enough to qualify under the rule - would this work, do you think?