execute my php code before every php call

Hi all, I have a simple code that override some env vars but i need it to run before any other php code on every php execution. I would like to avoid any change of all php code (even if its only to include the include command). Any one knows of such way ? I dont mind overriding this vars on php configuration file but i dont have any control of it as its should work on even the most strict web hosting (that still allow env vars manipulation) Any alternatives ? Thanks, TL