Supporting a plant in a plant pot container

I have my first Cymbidium. It is a tall sturdy variety with three flower stalks and was supplied in a narrrow but tall plastic pot. As we wish to have it in the lounge whilst it is in bloom, in order to 'hide' the pot the container had to be quite deep and, as a consequence, has quite a large diameter too. The plant is standing on clay pebbles to keep a good humidity level around it but lacks stability when moving it into and away from the window in order to give it good winter light but away from the curtains at night.
If we lived near a suitable beach I would place large pebbles around it to hold it upright but our local beach is pure sand only. Has anyone any suggestions for what best to fill the space between th pot and the container whilst still providing for the humidity from the pebbles to reach the plant?

 

Have you got any expanded polystyrene from old packaging? You could wedge it around the pot. Failing that, I'd use an old wire coat hanger bent into u shapes to keep the inner pot equidistant from outer