Also, with other plugins one can set the # of window panes, divided by mullions/muntins. Is that the same question as was recently posted here? To which was answered:
...What I would recommend to do is to to not insert the panes using the Edit Window Tool but instead draw the different size panes using SketchUp tools then creating the panes as a group or component and colour it to match the rest of the window...
It would work of course, but it seems like something that could be integrated (tricky for his uneven window sizes maybe).