Weighing down the machine?

I work in a care home and recently I took my machine into work for one of the residents to try it. She loved it as she only has use of one of her hands and can't otherwise knit or crochet.

The main problem is that the suction cups can't really stick to all the surfaces we use in the home and she can't hold it down with one hand and turn the crank with the other. Does anyone have a way of weighing down the machine to stop it moving without having to use both hands?