Caching dynamic pages / excluding parts from caching

Ok, the solution was fragment caching.First you have to set your secret phrase by setting

define('W3TC_DYNAMIC_SECURITY', 'my_string');

in wp-config.php and then you can use PHP code like this

<!-- mfunc echo "Hello World<br/>"; --><!-- /mfunc -->

which outputs this dynamic code

<?php echo "Hello World<br/>"; ?>

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