CPack with externally created .app bundle (macOS)?

I’ve manually done lots that CMake+CPack are meant to do for me, here are the summary of my hacks, hidden behind an if(BUILD_APPLE_BUNDLE) option flag:

set(CMAKE_LIBRARY_OUTPUT_DIRECTORY
     "${CMAKE_BINARY_DIR}/${EXEC_NAME}.app/Contents/PlugIns")
set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY "${CMAKE_LIBRARY_OUTPUT_DIRECTORY}")
set_target_properties(
            "${EXEC_NAME}"
            PROPERTIES
            MACOSX_BUNDLE_NAME                             "${EXEC_NAME}"
            MACOSX_BUNDLE_VERSION                          "${PROJECT_VERSION}"
            MACOSX_BUNDLE_GUI_IDENTIFIER                   "org.${EXEC_NAME}.gui"
            MACOSX_BUNDLE_ICON_FILE                        "Icon.icns"
            MACOSX_BUNDLE_INFO_PLIST                       "${CMAKE_SOURCE_DIR}/cmake/Info.plist.in"
            MACOSX_BUNDLE                                  "TRUE"
            # MACHO_COMPATIBILITY_VERSION                  "12.0.0"
            RESOURCE                                       "${RESOURCE_FILES}"
            XCODE_ATTRIBUTE_CODE_SIGN_IDENTITY             ""
            XCODE_ATTRIBUTE_CODE_SIGNING_REQUIRED          NO
            XCODE_ATTRIBUTE_DEBUG_INFORMATION_FORMAT       dwarf
            XCODE_ATTRIBUTE_GCC_INLINES_ARE_PRIVATE_EXTERN YES
            XCODE_ATTRIBUTE_CLANG_LINK_OBJC_RUNTIME        NO
)
add_custom_command(
        TARGET "${EXEC_NAME}" POST_BUILD
        COMMAND install_name_tool
                -rpath "${CMAKE_BINARY_DIR}/${EXEC_NAME}.app/Contents/PlugIns" '@executable_path/../PlugIns'
                "${CMAKE_BINARY_DIR}/${EXEC_NAME}.app/Contents/MacOS/${EXEC_NAME}"
        WORKING_DIRECTORY "${CMAKE_BINARY_DIR}"
        COMMENT "Replace library search path from absolute to relative"
)

Which works great (finally!). Unfortunately I haven’t figured out to make it play nicely with CPack.

Before I started building my own macOS .app bundles “manually” I did have this code in place:

install(TARGETS "${EXEC_NAME}" "${PROJECT_NAME}_lib"
            # TYPE "RUNTIME"
            RUNTIME DESTINATION "${CMAKE_INSTALL_BINDIR}"
            LIBRARY DESTINATION "${CMAKE_INSTALL_LIBDIR}"
            ARCHIVE DESTINATION "${CMAKE_INSTALL_LIBDIR}/static"
            BUNDLE DESTINATION  "${CMAKE_INSTALL_BINDIR}/${EXEC_NAME}.app"
            COMPONENT           "${PROJECT_NAME}")

But now that [obviously] puts my .app within another .app; which doesn’t work.

Can I get some sort of trick like this working?

install(DIRECTORY "${CMAKE_BINARY_DIR}/${EXEC_NAME}.app" DESTINATION .)

Would be great to generate .dmg and .pkg (otherwise I’ll have to manually generate those also!!!)