As an update, I can report that our homeschooling efforts have taken the following form:
Older Daughter has a package of homework that was sent with her by Friends Omphalos. She does the work just as grudgingly and last-minute as she would have done at home.
I have walked Younger Daughter through a few pages of Singapore Math, and all of us have at different times helped her read a few of her leveled readers.
Every day we spend on our travels I find myself becoming more of an unschooler. The most mundane of our activities here -- for instance, biking around the small city where we now live, which we've been doing a lot -- seems so much more valuable than most of what the kids did at school.