Regarding telling the CBP officer that the foreign country needs it, just don't tell them that. Tell them you want to be sure you don't get forced to pay duty on an item you owned prior to leaving the USA. They've no recourse, that's it's purpose as already stated.
My own experiences have actually been much easier. The CBP office at Phoenix Sky Harbor is not at the main terminals. I've never once waited in line, only a few moments for an officer to finish what they were doing and then they came and helped me out with no issue whatsoever.
There is also a very small regional airport in the east valley which is actually closer to my home. It's been just as easy, albeit one incident. One year I went into the office first without my rifles and told the officer why I was there. He asked where are the rifles? I said I wanted to tell you fist so that I didn't cause an incident. He laughed and told me I didn't need to worry.
So the next time I just strolled right on in with my rifles cased. The lady in the office nearly came unglued when I told her what I had and she admonished me to first let them know before I bring them in next time........