Well, than get the Child Support Committee to change the guidelines to reduce the Child Support gross income number by the documented amount of Social Security and Medicare, etc. for EVERYONE.
There is an explanation in the Child Support Guidelines that non taxable benefits are not considered to be part of the Child Support income number. I suppose a self employed person might argue that the amount in excess of what a non self employed person would pay, the employers portion, would be considered a non taxable benefit and thus a business expense. I still think that is a tough argument to make due to the technicality of the calculations required to determine the amount of $ difference between what a self employed person would pay over what a non self employed persons would pay.
Additionally, it would be difficult for the Court to determine whether this was an expense of your business which may be taxed separately as a business with you as an employee of that business or an independent contractor of that business or a "self employed" filer. Not my area of expertise. Definitely worth asking an accountant if the additional Child Support on 7.5% higher income would be a high enough $ value to justify all the extra paperwork and expense explaining it to the Court.