C# Web Application - Shared Master Page

We have a company intranet project and we want to have sub-projects off of that so that we can deploy sub-projects independently.  The problem we have is that we want to have the sub-projects use the master page from the parent project.  We included a reference to the main project and so the types resolve correctly, but when we try to run we get errors that the master file cannot be found.  How do we set things up so that we do not have to include a copy of the master page in every project?  We don't want to have to update 1001 master files every time we modify the design of the root master.  We also have the same problem with user controls, however I am confident that whatever works to solve it for master pages will work for the controls as well.