Has the suspension been lowered in any way? If so, the alignment parameters are different from the factory settings.
If not, you may still need a rear wheel alignment anyway...improper rear suspension setup can cause you to go through rear tires in a hurry!
Aggressive driving habits are helping the cause as well, and that may well be why you need to be on top of the alignment thing. Nobody makes a tire that can take extended shalom-like punishment for very long...sticky tires leave a lot of tread on the road, which is why pros change tires so often.
You can go with Dunlops or Contis, as I find they go a bit longer than Michelins, and are less expensive, but the tradeoff is that handling is compromised a bit.
But until you tone down your driving techniques, expect to replace tires often...