Cursorkeynavigation in a user interface?

Hello there!

I’m trying to get an user interface done in v4, so nice that there are nodes like Buttons and sliders and such stuff, but I want to control a kind of cursor/focus with the Arrowkeys on the Keyboard.
This Cursor should highlight quads which are aligned in a grid, but they are different in size, so when i press a key it should highlight the corresponding element in the right direction.

for better understanding, here is an example:

I was trying with GridPick and a normal Button node, but they aren’t that flexible.

So does anybody know how to get this done?
thanx, andi