A good engraving shop should be able to handle something with a uniform radius. My brother was involved with some of this a few years back and I was impressed with the range of objects they were able to handle. I hadn't expected anything much beyond flat items, but they seem to be able to cope with more than that now.
I will also add that those billet aluminum shift knobs look quite nice, but are anything but pleasant in either the summer or the winter. I put one in my GTA (5 speed) and wound up putting a sock over it. I was either freezing my palm or burning it. It was a pain. Literally. The next time I want a custom shift know I am going to turn one out of wood.