I have a bad ankle, the result of a tri-malleolar fracture. My personal experience is that, yes, it's not walking it's standing that cause me pain and swelling. That and stairs (plus it gives out so I'm prone to falling).
My advice (depending on the type of injury) and what I do, is to have him take Ibuprofen upon waking and every 4 hours through the day, regardless of how the ankle feels. If he wants to add any pain meds to that, do so. Mine zones me out so I usually don't. Whenever he's sitting rotate his foot/ankle. I also wear a light brace that provides support and I never take it off. It seems to not only provide some comfort and support, it also helps prevent swelling. When he gets back to the room at night, elevate the ankle and ice that puppy down (10 mins on, 10 mins off for 30-45 mins), take more Ibuprofen and pain meds.
If you normally do a mid-day break, ice it then too.
I've done 6 days straight this way with minimal swelling or stiffness at the end of the trip.