Zend certified PHP/Magento developer

Catalog price rule and tier pricing

How to have catalog price an d tier pricing working together?

I have a product that is tier priced eg. Buy 2 get 10% discount, buy 4 get 20%. I also sometimes put the product on discount through catalog price rule eg. -20%. When this is on the tier pricing is not effective. How do I make that both of them are effective eg. buy 4 get -20% tier price discount and 20% special discount?