Hallo - You may know this one already but for those of you who don't, here it is!
Standing tall, have the ball in front of you and place 1 foot on top of it. Roll the ball away from you so leg becomes straight and then back in so leg becomes bent. Do these a few times so people get the feel of it.
Then you can bring in front raise arms to co-ordinate with the legs and after a few of these, as you roll the ball away you bend the supporting leg as if doing a one leg squat, roll the ball in and stand up into the starting position etc.
Repeat on other leg.
If desired you could use hand-weights or dumb-bells for the front raise, depends how hard you want it to be or what you want them to concentrate on !
Thanks - Spotty Dog