Organize Content Pipeline in Visual Studio

Question

(This is not about the XNA Content Pipeline)

I'm trying to implement a content pipeline using Visual studio, that is:

1. Project A produces file a
2. Project B produces file b
3. a and b are passed to an external compression tool which produces output files a' and b'
4. a', b' and some additional meta information are passed to Project C merging it into file c
5. c is finally passed to the actual Project D

This entire process from A/B to D takes roughly 10 to 20 minutes. Naturally I want this to be executed as rarely as possible in order to be able to keep working on any of those projects without too much downtime. The pipeline should also be easily extendible.

As is, the entire pipeline is executed using various command line calls in a VS10 Makefile project. Thus the pipeline runs each time I build the solution, even if the content files or projects didn't even change at all.

Obviously that's not the smartest way to do it, so what's the usual approach to issues like this? Custom Build Steps? Batch files?