So I read this, and I thought, "How do you get mice to jump up and down?" and after a moment realized the answer was probably "Food."
In the meantime, the current state-of-the-science message about exercise and bone building may be that, silly as it sounds, the best exercise is to simply jump up and down, for as long as the downstairs neighbor will tolerate. “Jumping is great, if your bones are strong enough to begin with,” Dr. Barry says. “You probably don’t need to do a lot either.” (If you have any history of fractures or a family history of osteoporosis, check with a physician before jumping.) In studies in Japan, having mice jump up and land 40 times during a week increased their bone density significantly after 24 weeks, a gain they maintained by hopping up and down only about 20 or 30 times each week after that.
Then I hopped up and down on each foot 20 times each. :)