I have a set of includes that reside in a far off directory meaning that including them requires a long include, such as:
#define DIR "../../Path/to/my/"
#define FILE1 "file.h"
#define FILE2 "anotherFile.h"
#include DIR FILE1 // should end up same as line in first example after pre-proc
You can't customise the search path for include files like this, but you can tell the compiler where to look for include files. Many compilers
-I option for that, e.g.:
gcc -c stuff.c -I/path/to/my/ -I/path/to/other/
If that makes your compilation command too long, you should write a Makefile or, if you are working in Visual Studio or similar IDE, customise the search path in your project settings.