PHP Filter and Caching

Hi,
i would like to analyse URL Parameters and write information of this to the session. Currently I use the hook_init for that, but this hook is not processed if the cache is activated. So this doesn't work at all.

Within a page I would like to analyse the session. Therfore i used the embeded PHP (php filter). But this is also not possible with cached pages. :-( . I tried to deactivate the filter cache by hacking the core module

function php_filter($op, $delta = 0, $format = -1, $text = '') {
....
case 'no cache':
// No caching for the PHP evaluator.
return true;
....
}

but still the same problem.

Could anyone give me some advice how i can solve my issue?

I have also an alternative idea but couldn't find information how i could get it done: add the url paramters to every link so that i don't have to use the sessions

Thanks for your help.