I found a very built-in and easy way to prompt a system-specific nice open file dialog:
import Tkinter from tkFileDialog import askopenfilename tk_root = Tki
There is a C library designed to perform this function, which could be wrapped in python.
https://github.com/mlabbe/nativefiledialog
Not sure what limitations the py2exe format imposes but I think this could be packaged into a pip wheel for example.