Perin nave you thought of asking the new member "child maintenance options" if anything can be done, the problem is those who are self employed can be hard to nail down as to what they really earn, and it is true some will have their income payed to a company often off shore that they then take loans from, they call it tax efficiency i call i dodgy, i think i read that the powers that be are keen to stop some of these sharp practices but right now they are legal, i would at least pm CMO and see what he has to say.
IF you think your ex has income which the main calculation didn''t take into account have you applied to the CSA for a variation? Diversion of income and lifestyle inconsistent with declared means are grounds for a variation.
1. Start your own limited company and listing your new girlfriend/boyfriend as your partner. Only they then take any money out of the business. Hence no income for the ex and the partner pays for everything and gives them cash.
2. Quit your job, get a P45, rent a flat overseas and then show the P45 and rental agreement to the CSA and they close your case. Then make sure no one tells your ex that you are back in the UK and working
3. Job hopping. Make it impossible for the CSA to know who your employer is and if necessary have mutiple umbrella companies that you work through and swap them every few weeks.