Template hooks at PHP hooks are different...you need to use a PHP hook to hook template code into a template hook. (If that makes sense.)

So, if I wanted to add some display code to the postbit without a template edit, I'd add a plugin to the postbit_display_complete hook (I believe off the top of my head.) and utilize one of the template hooks in the postbit.

I'll post some specific code if no one else does by the time I get back to my dorm.