Question about site.master files..

I've been an ASP.net programmers using primarily VB for years so I know my way around controls, elements, etc etc.. I have a question about site.master files. Basically on our network at my job over the years we've developed about 40-50 different in house apps but our major problem is we have to change the site master file for all of the apps anytime we make any design or code changes. What I'd like to know is if there's a way to make a centralized site.master file that I can point to from all of my apps or maybe an included or .dll file or has anyone had success using a different method to centralize the top header portion and main structure of their various web-sites. Did a search but everyone seems to skate around possible solutions..