I suspect the only way to do that would be to override the Additional Child Tax to $0.

I don't have any clients in this situation, but I also suspect the IRS may send the taxpayer a notice saying their tax return is wrong and try to make the taxpayer take the Additional Child Tax Credit.

Personally, I would suggest the client file the tax return properly by claiming the Additional Child Tax credit, but then they can donate it back to the government if they do not want to keep that part of the credit.

https://fiscal.treasury.gov/public/gifts-to-government.html

https://www.treasurydirect.gov/govt/resources/faq/faq_publicdebt.htm#DebtFinance