It's possible, but you need to be able to edit your own custom UI.
Recently I edited mine so the casting window looks like this:
Screen Shot 2015-10-27 at 8.18.55 PM.jpg
Had to edit both the font size and the window size (I'll have to change window size again since the longer spell names are still getting cut off).
Check out
http://eqinterface.com/ to learn how to modify UI files.