I misread you before.
AFAIK what you want is not possible, you can only have the countdown bar on the screen that shows the "default partition".
You can use Instant Menu=y to go straight to the graphical device selector. But Instant Menu=y will override the timeout setting..so you'll have to manually select which partition to boot.
Looks like you can have your cake, but someone else will be eating it for now.

/EDIT
Oh damn, I AM going crazy, we're in the
feature requests sub-forum. lol