Astropy has a nice description how arbitrary packages can be installed into the bundled version of CASA (all versions before 6): https://docs.astropy.org/en/stable/install.html#installing-astropy-into-casa
This works well but can be a bit annoying to restart CASA multiple times and wait in between. The following simple bash script solves this:
# packages to be installed
####################################################################################################
Using CASA can be slow at times. There are many tasks that have to work in a serial way and thus cannot be parallelized. Often, these tasks have to be run for a number of independent files which opens up an opportunity for a manual, kind of brute-force parallelization: just execute multiple instances of CASA and let each do only one specific task. This is quite easy to implement in python. The function run_in_casa in my python_helpers collection is a wrapper to launch CASA and pass commands to it. It takes the approach of passing the commands as a file to execute rather than directly connecting (e.g. to stdin). This is simple but robust and has worked very well for me for years. With this method to execute CASA, parallel instances can be created with the multiprocessing package.