Some European vehicle companies used to (and may still) have programs whereby one could purchase a vehicle over there, drive it around for a time and then (typically) return it to the factory, where it would then be modified as necessary to meet US DOT and EPA regulations, certified as such, and then shipped to the States. I recall for certain that BMW motorcycles, Saab autos, and I think Porsche/VW offered such programs, and may still do so. Other manufacturers may have had or have similar programs. It was a great way to get in a little fine European travel and have a big rolling souvenir of it later.
Somehow I doubt Royal Enfield has a similar program. For one thing, I am led to understand that foreign citizens may be barred for some reason from purchasing new vehicles in India, which explains why Noraly's first Himalayan, "Basanti", was, officially at least, owned by some Indian fellow from whom she "borrowed" it.
Still, yours seems like a fine idea. Were I to ponder such an adventure, I believe I might start by reaching out to the good folks at Royal Enfield of North America in Milwaukee to ask what they might suggest towards getting it done. At least the folks in Chennai might answer an email from RENA, whereas my own personal experience leads me to believe they'd never respond to yours.