[CMake] Per-configuration include directories?

[Kevin Burge]

I'm trying to get my large project (built of many sub-projects and 
external projects) to build correctly in Visual Studio, allowing the 
user to compile release/debug from the UI.  One problem I have: I'm 
building an external library, and I've customized ExternalProject to 
keep per-configuration builds of the external projects.  The problem I'm 
now facing that I don't see a resolution to: I need include_directories 
to allow per-configuration includes.  I.e.

include_directories (third_party_INCLUDE_DIR_DEBUG)

or

include_directories (third_party_INCLUDE_DIR_RELEASE)

I tried setting COMPILE_FLAGS with -I... for the target, but cmake seems 
to ignore that when generating the Visual Studio 2005 project files.  
There doesn't seem to be a way to force the include into the visual 
studio project files.

Is there a way I can do this?

Thanks,
Kevin