This is a nice idea, but I don't think it's at all possible. Looking at Occupy and other large protest movements in recent memory, none of them were really above reproach to this degree, at least not once they reached scale.
I still remember the SF Occupy camp. Civilized, respectable, clean, and considerate lasted about two days. You put 500 modern, young protesters on a beach and "clean, civilized, respectable, considerate" will be a distant memory.
In the grand scheme of things, I'd argue that occupying a beach to stick it to the man isn't a great way to spend time.
An "Occupy Malibu" protest needn't suck resources from cancer research. A few hundred (thousand) people are going to be visiting beaches in the general area of Malibu anyway. A concerted effort by beach-goers to find and use the most egregiously obstructed public beaches (for instance, using this app) could be both satisfying and low-cost.
Not sure what the point of it all was, since there are many other nice public beaches. Maybe it was worth it just pissing off a bunch of people with sticks up their collective asses?