The app thing makes a WHOLE lot of sense if you've done the ipad mini dash installation...
Having done it, the problem is that when driving I would much rather find the window button with just my touch feeling and press it to lower my windows, rather than try to find a software button on the screen.
It really isnt so bad though: ipad mini to a supported bluetooth receiver, connected to your favorite microcontroller which intercepts your window signal wires and controls them.
Or beef up your microcontroller selectino and run voice recognition, always listening for key phrases and do anything you can think of by voice control, like lower the top or windows
