Steve,
I am please that you were successful with your right to work protest, but I don't think the 'mob' tactic that worked for you could work for the fuel prices;
Referring back to my earlier post, I made the point with so many 'bosses' in the oil industry to focus on it dilutes the effect of what you propose, compared to your situation where you only had one boss to impress. He also knew that if you all decided not to stay with the company, he would have a major problem recruiting enough skilled people quickly enough to cover your jobs and experience. That would threaten his business so your action was able to weaken the boss's resolve.
By comparison, a 30min stand still of all traffic would only marginally affect the companies involved, but it would inconvenience to some major degree lots ordinary people, not to mention the emergency services. Who would end up paying - the public in lost earning, possible threats t job security etc.
From the oil company's point of view, all the companies would be equally affected so there would be no commercial pressure for any of them to break ranks, because they all know that very quickly the British public would be moving on and needing to buy fuel.
Now more effective approach may be to focus on one company and nationally decline to purchase fuel from any of their outlets for an extended period (a week or more perhaps) them move onto another brand, and so on. Another option is having knowledge of where the keenest price for fuel may help but it needs every one to know and to boycott the high price stations. But even that has its problems, where for example this is only one filling station within a significant area and people have little or no choice but to use it.
So there is no simple approach to bring pressure to bear on these multiple companies.