My friend suggested that Truman could have targeted Mt. Fuji (though he didn't realize its proximity to Tokyo) in an effort to demonstrate nuclear capability without the ethical or moral dilemma of bombing major cities. Somewhere like Hokkaido or off the coast might be appropriate, I suppose.
Could they? Yes. Did they think about it? A little bit, at levels far below Truman. Did anyone in power take it very seriously? Not really. Lots of details here.
There was no dilemma, we were already doing it with fleets of bombers dropping napalm on major cities, it was just a better bomb