I´m a big fan for excercise and I guess that the threadstarter is already working out (or atleast trains aikido) on a regular basis (hence "outside your normal training schedule"). But in my experience it´s easier to slim down
by focusing on my diet than by more exercise.
A intermediate heart rate monitor will estimate the amount of burned calories according to your data and your heartrate during practise.
Like this one: http://www.suunto.com/suunto/Worlds/...=1187809285803
An interesting article on the hazards of maintaining your weight through diet alone:
Even if you don't lose any weight through your exercise program at least you improve your fitness and health levels.