What is the trick to make Visual Studio 2008 use project relative paths for include directories, etc.?

I have a Visual Studio 2008 solution with around 10 开发者_运维知识库projects. When I add include directories by launching browse popup and select a directory, I see Visual Studio storing the absolute path in the project file. What I want it to do is use project-relative paths even for paths in sibling folders.

Is there a setting in Visual Studio to force it?

No, there isn't: the browse button opens the standard open file dialog, this returns full paths, and Visual Studio just uses that. You'll have to enter the paths manually, or create a macro/addin that resolves the relative pahts.