[Typo3] third party cookies

[silk]

Hi everyone,
I run TYPO3 in a subdirectory on site1, but i need to give access to the BE 
and FE using a frameset on Site2 (an other website).

I get cookies blocked by IE6+, because of third party cookies policy, so 
it's impossible to login from the site2

I need to add an html header to ALL the output of typo3 (BE+FE)

in PHP I can do it with
<?php header('P3P: CP="myPrivacyPolicy"'); ?>


somebody knows how to do it?
I'm quite new to typo, thanks anyone who helps me.
---------------------------
Lorenzo Garassino
---------------------------