By working a healthy 8 hours a day, and integrating walking into their everyday activities: walk to the store instead of taking the car or getting things delivered, for example. Although I do agree that it depends on the environment you live in - whenever I found myself in dense built-up inner-city neighborhoods with a lack of green, my step average was just half of what it was in more walkable, leafier neighborhoods. While not having lived there myself, I imaging US suburbs would be equally detrimental to my walking habits.

But going from grocery delivery to walking to the store is not integrating it into your everyday activity. That's restructuring your life. Sure, I could walk to work and back every day I go to the office, but it'd be 45 minutes a day. That's a highly non-trivial time investment. And it wouldn't get me the equivalent of what I get from my under-the-desk treadmill, which requires a time investment of approximately zero.

My only wish is that I could do some Pokemon style exp-share so I could distribute the muscle gain to the rest of my body ;)

Probably won't get you the equivalent of 8-10 miles a day, but you can buy some dumbbells, put them by your desk, and do a set of something every hour or so during a break. I aspire to do this, but often forget/get too lazy to do it often enough.