My advice would be to seek a fairer assessment rather than a loop hole, to avoid any suggestions your motives are dishonorable. (Whiter the white).
Presumably you've had the phone call with the Child Maintenance Service and the decision of how much you pay is proportionate and considers your earnings based on the previous tax year and the amount of time your daughter stays with you?
Does it also consider your daughter "doesn't go without anything" when in your care? What does that refer too? Do you keep receipts?
One of my favourite Child Maintenance success stories was from an older friend of mine who had a daughter with is ex wife in the early 90's. There were no contact disputes when they separated when the child was one year old, and they agreed on a really good child arrangement out of court that was maintained right up until the daughter turned 16 years old with no problems (a rare case of mutual peace and cooperation), but he totally ignored the old Child Support Agency letters that he received every couple of months, shortly after he left the home he shared with them as his view was that he bought the girl everything she ever needed, so didn't need to pay.
Even when the Child Support Agency contacted the mother she informed them that he bought the girl everything she needed and didn't feel the need to make a claim. She even refused to disclose the fathers place of work. But obviously the Child Support Agency didn't see things this way.
Every couple of years he moved due to work, and a few months after moving in, a typical cheap, brown letter from the Child Support Agency would appear on the doormat with an ever increasing amount of outstanding Child Maintenance arrears. But he continued to ignore them.
Only once did his employer at the time call him into the managers office to inform him that the Child Support Agency had been in touch and they had to start deducting his wages. So he did pay via a Deduction of Earnings Order for a few months, but then left that job and went to work somewhere else. I don't know how but the Child Support Agency never caught up with him and the Deduction of Earnings Order didn't follow him either.
Fast forward 15 years and the daughter is growing up. She asks dad if she can spend more time hanging out with her friends and slowly but surely the child arrangement comes to and end with the daughter going to visit dad once a week on her terms.
After finally saving enough to buy his own home and going on the Electoral Register so he can vote, guess what comes through the post?
A letter from the Child Support Agency, and a bill for £12,000 in child maintenance arrears!!
It was at this point that he knew he couldn't avoid the matter anymore. He wasn't going to be moving again for the rest of his life. So he went through all his bank statements for as far back as he could and somehow managed to work out that in the 15 years he should of been paying maintenance he spent £21,000 on his daughter. Not only did he manage to compile almost 15 years of bank statements, he kept a shoe box in the attic with receipts for every piece of clothing he ever bought her. Every school uniform. Every pair of shoes. Every school meals bill. Every school trip. Every holiday, just in case the mother ever did decide to dispute things.
He sent all this in a large A4 envelope to the Child Support Agency with a letter which read:
I dispute the claim from the Child Support Agency that I must pay £12,000 in outstanding child maintenance payments, as throughout my daughters childhood I have contributed £21,000 to her upbringing. (Pleas see evidence enlcosed).
I have calculated that I owe the Child Support Agency £0.
Yours sincerely...
Two weeks later he received a letter from the Child Support Agency in reply.
Dear Mr ....
Thank you for your letter dated ....
Your account has been closed.
You owe £0