I have used two large plastic containers (light and cheap) and put the machine on top and prop up the back a little to aim down into court.
two warnings though-
don't do it on a windy day b/c it can blow the setup over- you will see it is not as stable as if you used a cart
static electricity can build up since ontop of plastic, get some kind of metal chain to touch the ground. I blew out my circuit board after a few sessions of this. I was noticing a shock everytime I turned off the machine with this setup prior.
Silent partner owners- you know that little metal chain at the bottom of the machine? It actually has a use-to ground the machine to prevent static build up.