If most of the companies emit 400% of the allocated CO2 quota and you 10% of the quota, statistically your usage can't compensate for the scam that's going on with the current incentives :(
You're right. This is why not cars, but fuel - you know, like the source of the carbon - should be controlled/taxed. I also think that any car can be driven in an inefficient manner. The 1.7t PHEV I use has been amazing in terms of fuel economy, but I know people that burn more fuel in their hybrids than in V8 ICE sportcars.