Generator expression for project name?

Code
1

I use the superbuild approach to build and install dependencies with ExternalProject_Add. Since I have some common CMake options, I factor them out in the main CMakeLists.txt. For instance, to install the dependencies in a common directory install/, and within that directory under the subdirectory based on the project name, I add

"-DCMAKE_INSTALL_PREFIX=${CMAKE_SOURCE_DIR}/install/$<PROJECT_NAME>"

to CMAKE_ARGS, expecting an install tree like this:

${CMAKE_SOURCE_DIR}
|- install
|  |- depencency1  # the name depencency1 deduced from PROJECT_NAME
|  |  |- ...  # installed artifacts
|  |- ...
|  |- dependencyN  # the name depencencyN deduced from PROJECT_NAME
|  |  |- ...  # installed artifacts

Unfortunately, PROJECT_NAME is not accepted as a generator expression.
How can I achieve the desired install tree structure above?
An alternative is to add

"-DCMAKE_INSTALL_PREFIX=${CMAKE_SOURCE_DIR}/install/${PROJECT_NAME}"

to CMAKE_ARGS in the subprojects, but that would mean duplication for each subproject, so I would have to modify all of them if I change my mind and choose a different base install directory.