This is an issue for you and your classmates to work out.
When I did my MBA and we drove from NL to Switzerland and back and were caught on a speed camera (they're very common in Switzerland), we agreed to share the 100 Euro fine.
If he gets multiple fines, then I think thats on him to pay -- it will be on your credit card so you'll have to lean on him to pay. Hopefully a reasonable person will accept responsibility. But its not up to Avis or to those traffic authorities.