I had the same problem some years ago on a Nourish crank that had the mainshaft slightly undersize, only .001" or so, as I recall. I had the area where the race fits hard chrome plated just enough to get to the low end of the original .0001" - .0004" fit. Because the plating was so thin, no grinding was required. The platers have enough knowledge about their plating rates to be able to get the specified thckness of chrome by adjusting the time in the plating bath. Also, with such thin plating, there is no risk of hydrogen embrittlement, as there would be if you ground the shaft undersize and built up a significant amount of chrome.
It worked perfectly, and the crank is still in use on a 920 race engine today.
I wouldn't suggest copper plating. I was told by the plating company, who had extensive experience with repairing crankshafts, that it would work for a while, but was too soft for a long-term repair.
I've also tried the Locktite bearing mount, and had the same experience. It won't hold for long.
Metal spray would also probably work, but I haven't tried it myself. From sprayed parts I've seen, it is rough enough that you would probably have to polish or grind it down to size.