If I understand your question, you have one solution file with 25 projects and there are many project references between projects. And you'd like to open just one of the project which currently has project references but be able to open and run it without actually opening the full solution (and all 25 projects)?
There is no way that I know of if you use the same project file. The project stores the references. That means they must be Project OR File, but not either/or.
I haven't tried this, but you should be able to create a second project file that uses the same source files (maybe a different project name?), one has file references and one has project references. I don't know if that will work or not and you might have to play around a lot.
What we've done is to use project references for only 2 or 3 projects when needed (for debugging to be able to walk through a referenced project). At some point you should be able to compile 24 of your projects into DLLs and use those references. By "some point" I mean when the referenced projects are stable enough that you don't need the ability to step into them.
-Nerseus