Have you considered a recumbent bicycle or tricycle for him? They are more expensive, but sometimes good deals on used ones can be found on craigslist or ebay. I know he would want to test ride before buying to make sure it would work, but it seems like that would be a more comfortable solution for his back issues than an upright bike, even with suspension.
Where in Ashe County are you moving? My mother and step-dad own a vacation cabin outside of Jefferson/Lansing, and my DH and I own the lot next door, right on the North Fork of the New River. Looks like we're going to have to sell soon, as my step-dad is in failing health.
We have had many fun times there over the years and love the Virginia Creeper Trail. That's the only place we've ridden there other than short rides on the (unpaved) neighborhood road on our mountain bikes as the paved roads tend to be narrow, curvy, and very steep. We were much more comfortable riding mountain bikes with suspension on the Creeper Trail, as it can be bumpy in places. We tried it with our Bike Friday folding road bikes, which have wider tires than standard road bikes, and found those pretty uncomfortable, especially on our hands when going in the downhill direction. Front suspension is a real help with all the vibration.
Good luck in your move and bike search!
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow