How to refer to external SubRepo in the .hgsub file?

Question

I want to add a SubRepo which is outside the folder of the MainRepo as this SubRepo will be the SubRepo of many Big Main Repos at the same time for a certain design purpose. Example: Main is a big Repo Main2 is a big Repo my_lib is a subRepo for both Main and Main2 Repos

Main .hgsub:

../../my_lib = server_path

Main2 .hgsub:

../../my_lib = server_path

But mercurial doesn't allow relative paths to be outside of the Big Repo.

Is there any possible way to add the SubRepos outside the Main Repo ?