If I work illegally can I add my income to the household income and tell USCIS about it?

I hope you realize that working with authorization in the United States is a crime and unless the Obama Amnesty passes, you are in violation of the American laws.  Now, if you were submitting an affidavit of support and wish to show your income from illegal employment, you are clearly providing evidence to the authorities of your illegal behavior, generally speaking, not a good idea.  While adding this income to the household income would not necessarily trigger an investigation of criminal activity (the US Government apparently does not care much these days about illegal employment), but if something else leads to your investigation, this information will become solid evidence that will be used against you during prosecution.