It's a total pain to navigate all these state websites for registering our company and his employment. They are all different / UX is crap / terminology seemingly varies . . . I hate it.
Do you know of any service out there that's kind of like a Legal Zoom for state employment filings? I can't find anything through search.
In an ideal world the Federal Government would just operate a hub and there would be a universal business record service that you could drag and drop the US State entities where you company operates. Until then a third party service would be awesome.
What you could do is have him declare a home state (primary residence), maybe his parents state or something, and as long as he isn't spending long periods in another state he would be considered a traveler and not subject to local state employment taxes generally. Of course, if he gets a new drivers license etc then that won't work. This is how you handle traveling consultants who might literally spend the next 6-9 months in one state for a job, but they are permanent residents of their "home" state for tax purposes etc. He can even have mail temporarily forwarded to the state he is in, just not permanently forwarded.
You should probably talk to an attorney or tax accountant just to get the details right, but I did this for years with my consulting teams and we were always on the right side of the law. Only place that it gets more tricky is the north east area with their shared burden on taxes etc. But if he can avoid his home state being one of those then you are probably pretty safe.