There's no straightforward approach for this, because you cannot modify the Dataproc cluster used in the execution within the pipeline. So, if you really need to use the Python plug-in in Native mode, my suggestion is to create a cluster with the py4j library, and then connect it to Data Fusion using the "Remote Hadoop provisioner".
Consider that to use this provisioner, you'll need to create a new Compute Profile, which is only available in Data Fusion Enterprise version.
To install the py4j library in your cluster, you can either create a custom image with the library, provide an initialization actions script to install it, or SSH into the machines and manually execute the pip install command.