How To Disable Cache Headers

Hi, It's great that there are new cache-header features in PHP4, but how do I turn them off? I need to be able to control caching on a page-per-page basis -- some pages are cacheable, others are not. Turning off the directives in php.ini does not stop PHP4 from sending cache headers, which conflict with the ones I try to send. I don't see any runtime functions documented which would disable cache headers. Am I missing something? Ciao, Andreas