Thanks for the replies, folks!
So Close, I don't think a sabbatical is a possibility, but at least this year I got him to take a 12-day vacation - as in, 12 days in a row off from work. He built sand castles with our daughter, we took long walks and went to state and national parks - it was awesome, and afterward, even he admitted that he needs to unplug from work now and then.
marble jane, Daisy, and Noodle, I think the nonprofit volunteering route is definitely a possibility, and in terms of him serving on a board, well, they should only be so lucky! He'd have them whipped into shape in no time! ;)
I've worked with a variety of nonprofit organizations over the years, including working as a volunteer coordinator, so I have a good perspective on nonprofits and how they work (or don't work, as the case may be...).
What I don't want to do is have him continue to work in retirement and then for us to be trapped because of his work schedule - little vacation time, not a flexible schedule, etc.
When we made one of our MNC moves, I looked for part-time work for nine months. He had just moved up to three weeks of vacation. I was getting ready to take a part-time secretarial position with the Red Cross that paid $6/hour and came with 5 days of vacation after 6 months on the job. He sat me down and suggested I not let my self-esteem issues affect our lives to that extent, and that I should just volunteer doing something I liked and we wouldn't worry about the money. I offered myself up as a volunteer to a local art cinema that produced a film festival... and they hired me instead, with very flexible hours and time off whenever I needed it.
So when the time comes, I may remind him of that conversation. Who knows what might come of it?