I had to ask Chat GPT to help me since nothing would work. The addon worked with the lines it gave me, maybe this can help you:
In CMD (as admin)
Here’s the quick one-liner you can paste directly into your Python REPL:
__import__('subprocess').check_call([__import__('sys').executable, '-m', 'pip', 'install', 'Pillow'])
If you also want to upgrade pip in one line:
__import__('subprocess').check_call([__import__('sys').executable, '-m', 'pip', 'install', '--upgrade', 'pip'])