How to add additional include paths to CMakeSettings.json to get IntelliSense to work?

I'm using Visual Studio 2019 16.7.2 to open a CMake project that uses header files and libs located inside an absolute C:\dependencies path. However, that path is never directly referenced in CMakeLists.txt, and is only used in a separate build script that ships with the project and executes successfully. This means that when working on the project within VS, IntelliSense fails to recognize the included headers from C:\dependencies\lib[A,B,...], e.g. #include <libA/header.h> will not find the header for autocomplete and similar features.

I am not supposed to modify the CMakeLists.txt directly. Instead, I would like to reference headers from C:\dependencies base path in an unversioned CMakeSettings.json file which would hopefully fix the IntelliSense issue. Here's what I tried but it didn't work:

• adding an include_directories variable:

 "variables": [
 {
        "name": "include_directories",
        "value": "C:/dependencies/libA/include C:/dependencies/libB/include"
        "type": "PATH"
 }]

• adding a CMAKE_CXX_FLAGS variable:

"variables": [
{
      "name": "CMAKE_CXX_FLAGS",
      "value": "-I C:/dependencies/libA/include C:/dependencies/libB/include"
}]

The path strings themselves are not an issue, e.g. "C:\dependencies\libA\include" contains a directory libA with the referenced headers.

Any ideas on how to get IntelliSense to recognize the headers successfully?