the exec() didn't work out. so i inserted
require_once("http://jakchat.com/code.php");
at the top of the PHP section in the custom island concerned -- which i presume imported all 400 lines of code, with all its functions -- and this seems to work. i have noticed no speed hits when using the system, using an update time of 4 minutes for testing purposes.
nonetheless, makes me a bit nervous putting so much complex code in that section ...