By getting what you want, you would lose a lot.
Visual C++ IntelliSense is based on a couple major presumptions
1. that you want good/usable results.
2. that your current IntelliSense compiland will present information related to the "configuration" you are currently in.
Because your current configuration has that preprocessor directive, you will not be able to get results from the #ifndef region.
The reason makes sense if you think it through. What if the IntelliSense compiler just tried to compile the region you were in, regardless of #ifdef regions? You would get nonsense and non-compilable code. It would not be able to make heads or tails of your compiland.
I can imagine a very complex solution where it runs a smaller (new) parse on the region you are in, with only that region being assumed to be part of the compiland. However, there are so many holes in this approach (like nothing in that region being declared/defined) that this possible approach would immediately frustrate you, except in very very simple scenarios.
Generally it's best to avoid logic in #ifdef regions, and instead to delegate the usage of parameterized compilation to entire functions, so that the front-end of the compiler is always compiling those modules, but the linker/optimizer will select the correct OBJ later on.
Hope that helps,
Will