Insert the same functionality in different aspxs

Hello,

I'm trying to add a new functionality to an already created web. What I need is to let the users log out from every page in my web, but there are about 100 different aspx and I want to do it without replicating the code 100 times.

Does anybody know a way to do this? I've been thinking about it several days, but I don't find any solution that doesn't imply the modification of the .aspx and the .cs.aspx files.

Thanks in advance. ...