McCain's Separate Finances

Josh Marshall notes that McCain has been paying a bargain rate for the use of his wife's private jet, then asks,

Reading the piece, one question that suggests itself is why go through all the roundabout? McCain's wife can give him as much free air travel as she wants. That's just self-financing, which lots of candidates do completely legally. John Kerry, remember, took a loan out on his home to pour money into his campaign during its nadir just before Iowa. But remember, this was also around the time that McCain was kinda sorta opting in to the public financing system. So I'd be curious to hear how these two things would have interacted, what the legal repercussions would have been.

I suspect this has less to do with public financing than it does with McCain's desire to keep secret his wife's wealth and tax returns. His campaign's claim, "Senator and Mrs. McCain have kept their personal finances separate throughout their 27-year marriage", becomes less viable if she's making him six figure gifts or loans to support his campaign.