Like you see on websites sometimes, hovering with the mouse will unfold it (which creates a horrendously nervous user interface when no delay is used). You could give it a try with the lcd object. All tools are there: writing, mouse tracking, changing size.
You are right: [lcd] cannot expand [umenu] but I think what Johan meant was that you could code your own [umenu] replacement with [lcd] that does exactly what you want. The [jsui] object would be another option.
the java "robot" class will work cross-platform though.
also there is the
;max pupdate $1 $2
message which will move your mouse wherever. add the robot class and you can auto-click anywhere you want, including the Shut Down command for your computer...or someone else's if you get into networking. evil and fun!