Create symlinks for directories that don't exist - Windows

Question

I got this as my main directory.

└───etc_core
    └───modules_core
        ├───core_module_1
        ├───core_module_2
        └───core_module_3

I got another directory with the same structure, but with different modules.

└───etc_custom
    └───modules_custom
        ├───custom_module_1
        ├───custom_module_2
        └───custom_module_3

Desired structure

└───etc_core
    └───modules_core
        ├───core_module_1
        ├───core_module_2
        ├───core_module_3
        ├───custom_module_1 (link to etc_custom/modules_custom/custom_module_1/)
        ├───custom_module_2 (link to etc_custom/modules_custom/custom_module_2/)
        └───custom_module_3 (link to etc_custom/modules_custom/custom_module_3/)

Without symlinking each module, is there any easy way to mount etc_custom/modules_custom onto etc_core/modules_core recursively?