Sorry, EBS, but I think you just shot yourself in the proverbial foot.
The UN is supposed to be an independent body, not a sycophant of any national power.
The long and short of it is that if the US wishes to continue to utilize the UN as a political instrument, and holds back funding until it - the US - gets it's way, that's hardly in the original intent of the UN mandate.
The US entered into the present funding arrangement with the UN without coercsion, and is free to withdraw anytime it pleases. Undoubtedly, it would damage the UN, probably beyond repair. But what would that serve? Possibly isolationist conservative forces, but that's about it.
I don't like the fact that my car insurance is high... I don't like the fact that my electricity bill is creeping up and up... and I don't like the fact that my natural gas bill is being driven up by forces completely beyond my control... but the fact is that I've made an obligation to pay them on time, so I do.
Surely, the US, as the one and only superpower left on the planet, with all the military and moral suasion it possesses, can follow through on its own committments!