Installing unofficial extensions in JupyterHub

Hello, I would like to install some Jupyter extensions on top of JupyterHub. Until now I have been doing this in JupyterLab (jupyter labextension install <name>), but now I need to deploy a JpHub instance with the extensions installed for every user.

Specifically, I would like to extend the environment provided by the Docker image jupyterhub/jupyterhub.
How can I achieve this? Thank you!