I can;t really work out the full set up you have from your pic, but are you able to cover them with something to protect them such as cardboard or grass mats such as these ones
Rosewood Boredom Breaker, Small Animal Activity Toy Chill-n-Chew Mat: Amazon.co.uk: Pet Supplies
they will probably still be chewed and you will need to replace them but better than the plastic being chewed. you could also try putting ties or a plant pot in front of it if that works, as long as not too heavy and potential to fall on your hamster