What about a special treat to occupy him, like one of those treat puzzle kongs, or filled kong? We do this with our GSD when new people come over ( he's not very welcoming to strangers). We even build his anticipation by letting him see the treat beforehand, we put it on top of the fridge while we wait for the arrivals, then once people arrive he gets it. It's usually enough to keep him busy the first hour at least.
Some local libraries have small rooms that you can sign out. You could go there assuming they have a computer in the room or you have a laptop.
Is there a friend or family member nearby that he especially likes that could dote on him while you conduct your interview?
Otherwise, I'd follow IAPT's advice and give your dog whatever treat will occupy him the longest. And, I think your idea of taking him for a long walk first is a good one.
If he acts up I'm sure if you just apologise and can take care of him quickly, it won't be that big of deal.
I was thinking treat too. Take him on a long walk before to tire him out a bit (and maybe walk off any nerves you might have) and then give him the treat just before you start.
I had this very problem while I was unemployed last year. I had to do several phone screens and Simon (my dog) follows me everywhere. I could have took him on a 2 day walk and he would still want my attention, so when it was warm enough I went and sat outside and did the interview on my patio. When it was too cold for that, I kid you not, I went and sat in my car. I know it sounds crazy, but I didn't want to take the risk of anyone hearing my dog bark or make noises - it's unprofessional and distracting. Good luck!