wx.Config does not have those methods, I guess you meant wx.TopLevelWindow.
The way it works is that you implement a class that derives from wx.TopLevelWindow.GeometrySerializer and overrides the SaveField and RestoreField methods. Then you pass an instance of that to the top-level window methods. Unfortunately I see that there is a bug causing those methods to not be exposed properly to Python. I’ll add it to my todo list.