Hi Dean et al,
I also like sumo shiko, leg stomps (I only do about 100 per day, although Konishiki I read sugested 300-500 per day). The Nihon Sumo Kyokai has put together an exercise program for non-rikishi to follow here: http://www.sumo.or.jp/eng/kyokai/kenko_taiso.html
Lots of good stuff here.
Thanks for posting this Chris, I was just looking for something similar last week and came up dry.
To the OP:
I have two kids and a so I can completely relate to your question. Some solo training I can do around the house or work:
Running stairs at work
Walk or jog at lunch break
squats/lunges - whenever I have a few minutes and the though occurs to me
I'm fond of the pileates video training stuff. Most of them take 45 minutes to an hour, but the dvd's often have an express or targeted workout that runs 20 minutes or so. I can do them when we get the kids down and before I am ready for bed, mornings would work, too if you can get up an hour early. I can't.
I've been considering putting together a set of irregularly shaped weights for the house - just common stuff in relatively awkward packages - jugs of water, bags of sand, etc. I have some hope that this will help with my judo