I'd say if you really needed the extra part to reveal from the bottom, you can write a resize function which adjusts the position of all the elements in the figure during resize.
If it were me though, I'd just rearrange the GUI so the extra part expands on the right, eliminating any GUI element rearrangement issues.
Then again, I wouldn't be surprised if there was a clever workaround for keeping original elements in place when the figure expands that I'm unaware of.