1.) Add external tools and point to a batch file. Add the arguments listed below in the image. This assumes that your Git repository is one folder up from a 'Solution' directory.
2.) The batch file should have the following contents (Replace 'Administrator' with the appropriate user):
@echo off
echo Starting with switches: %*
echo.
echo.
C:\Users\Administrator\AppData\Local\GitHub\GitHub.appref-ms %*