Hello Jon, I don't think you would have any difficulty at all. Roynie and I bought bikes the first time we toured in the US (three and a half months) and simply used a friend's address to register them. Likewise, insurance was no problem. (Roynie even managed to total his first bike, claim on the insurance and buy a replacement so as not to have to cancel our trip.)
Having bought it in the US, keeping it there should not pose any problems - unlike a temporary import.
The only areas where I would advise caution would be unscrupulous dealers who might palm you off with last year's model or fail to offer any manufacturer rebate that might be going (as happened to us). And, in terms of insurance, make sure you take out the 'uninsured driver' cover to protect you in the event of a mishap - a large number of miscreant cagers turn out to be uninsured.
We actually intended to sell our bikes after our 2001 trip, but got it wrong and found that, in Oregon anyway, biking is a strictly summer pastime. Roynie's bike eventually sold after a year 'on consignment' at a Portland dealer, but we ended up shipping mine home to London. Since then, we have preferred to ship our own bikes to the US and back, but a Michigan-based friend is determined that we should keep a couple of bikes with him ... so we may end up doing the same as you.
Good luck. If I can be of any further help, ask away.