You can use a conditional on the Hold switch to change the displayed album art to be full screen. You'll need multiple copies of your album art at appropriate resolutions, though. You will also need to write your own theme, although I seem to recall a theme or two that do this already (I don't recall for which target). It's not quite what you asked for, but I think that's about as close as you'll be able to manage without modifying the source code and compiling your own build.