Even though this is years after the original question, this hit comes up when trying to use pip with maya and I didn't find any other instructions.
Fortunately, you CAN install pip and use it with maya! I've only done it with 2017 so far but image it will be the same for other versions.
1 - Download get-py.py from https://pip.pypa.io/en/stable/installing/
2 - Open a commandline to mayapy.exe (Generally in AutoDesk\Maya\20XX\bin) and run the file:
...Maya\2017\bin mayapy.exe get-pip.py
3 - It should run without any errors, and it will have added Autodesk\Maya\20xx\Python\Scripts\pip.exe
4 - Use this pip, just like a normal python install! Similarly, it places things in Autodesk\Maya20XX\Python\Lib\site-packages
So far most things seem to work correctly, like pytest, but jupyter doesn't.