How to filter PHP opener?

I've been searching the web and in this great forum but I didn't find anything.

I got some issue with a code higlighter plugin. Everything is fine except that some php tags do not work properly :

!--?php instead of ?php

It just breaks markup ! I only use HTML Editor.

How can I manage to make it work?

EDIT: in the meantime I just changed plugin and it works fine but I'm curious to know how to solve this issue. The plugin is Google Syntax Highlighter (verry old I know)