I think the way it could be decided is by first looking at cool vs. uncool and then the two groups in the winning category.  
Say we get 3 subzero, 4 cool, 4 uncool and 1 seriously uncool.  We would see that there are 7 votes on the cool side and 5 on the uncool.  So then we see cool has one more vote than subzero, so the car is cool.  If it was a tie, it would go in-between.  
The problem is that on Top Gear it worked kind of as a scale, so even under one category one car could be cooler than the other.  The best way to replicate this would probably be with a scale like Dragonistic's but where each member picks a number inside that scale.  But that would be a bit too complicated.