Comment 2 for bug 952132

A quick look into their documentation reveals the following:

Command Line Arguments
The following command line arguments are recognised. Note that these are implemented in "intpyapp.py", so should be pretty easy to change!

/run scriptname args
Runs the named script. Works just like "Python.exe scriptname args", except it is run in the GUI environment, and output goes to the interactive window.

/runargs scriptname args
As above, except the normal Pythonwin 'Run Script' dialog is shown.

I think you should try invoke pythonwin with `/run bzr ...` or `/runargs bzr ...` and see what happens. That could be an easy workaround.