Resize child components along with resized parent.

I often create mockups for dialogs and don't know in advance how wide the dialog should be to accommodate the different labels, etc. I know that I should add the Dialog/Window component last once the rest of the objects are in place, but I like to have it there so that it "feels" like a dialog while I create it ;)
It is often time-consuming to resize all of the fields to the longest one once I have added them all (or maybe I add a new field or change a label which affects the lengths). It would be nice to have the fields that are snapped to the inside edge snap lines to resize automatically when I resize the parent (e.g. Dialog/Window, Browser, or Rectangle/Canvas).

So, if I have something like this:

the Text Input field and Text Area would expand and contract with the Dialog/Window control (since they are snapped to the edges).