Only problem being yes, he'd need a smartphone that is not yet in evidence. But that's what Malletspace is for. Technical problems solved. The latest iPhones and Androids have the megapixel density to blow up the raw camera file that big if you framed it right. Check the color gamma and mark the cropping, input order, upload the picture file, Done.
Two, you need to be close to Anchorage or Juneau for Costco - but there probably is a similar service closer to wherever Doc is. They're using a simple Plotter size color printer, I know that Kinko's/FedEx Office has been doing that service for decades, when they were still just Kinko's Copy & Print.
Heck, there's a FedEx Office branch in Hollywood CA that can do you a Banner Print big enough for a Billboard, 12' wide (or high in Landscape) x (how long do you want), full color and everything. UV-Cure inks. Might take them an hour per 10' output though, it isn't all that zippy - I've watched it do full color.