The trick in this case is that, while you cannot resize a view presented using present, you could have another blank view be the one you present, and then the view you are resizing is a subview.
@polymerchm implemented this in a clean way, for use in settings menus, where he creates a semi-transparent view that dims whatever is on screen (could be another view), and creates a Fullscreen "shield" view. Inside that shield, you can have a subview that draws any other view wherever you want on the screen, and now can be resized like any other view.:
This concept can be extended to detect touches on the shield, to dismiss it when user taps outside the settings view.
Another option is to use my overlay class, which is designed for draggable window overlays.
Even if you don't use the actual draggable overlays, this shows how you can grab the pythonista app window root and add subviews the the main pythonista app window, that can live wherever you want and can be resized, however you have to take a little care in order to not crash things.