As darryn said, a random reverse grid doesn't seem very realistic. But yes, I can understand that the WTCC reverse grid is not THAT good too. So here's a few suggestions for that round 4 :
1)We can do a top 8 reverse grid, but not like WTCC, but like GP2, with only the half of the points of the heat 1 given to the finishers of the heat 2(so that mean, for example, 7,5 points will be given to the winner of heat 2, 7 points to the second, etc, etc, etc...)So with that rule, finishing in a good place in heat 1 will be more important than having a good place in heat 2, so nobody will want to finish 8th.
2)Another solution can be also to put some very short quali before heat 2(like 4-5 minutes). That can bring some very very big surprises in the grid, because with this rule it's very hard to deal with traffic.
3) Maybe my favorite one, I saw this system as I race the Hot Hatch Supercup yesterday, and it was very fun. So, before heat 2, you take a hat with some papers where are written all the numbers between 2 and 15, then you take a paper, for example : "10", and then that mean that the top 10 is reversed. That's a good solution I think, because there's absolutely no way to race specially to gets pole. With that rule, everybody will race the first heat "as it's the own race".
So, I hope everybody did understand me, I did my best with my very very poor english