Disable time limit on editing posts for first post in thread

[Timelord]

I like the idea of being able to prevent people from editing their posts after a certain amount of time, but at the same time, many users on my forum have threads that they actively maintain (i.e. post new content to the first post regularly). Is there any chance someone could throw something together for me that would allow me to disable the time limit on editing posts just for the first post in any given thread?

Thank you!