QUESTION: How can I make Gnome select GtkRadioButtons in the same group??

["Néstor Amigo Cairo" <nestorac gmail com>]

Hi, all!!
I have a little problem: I am developing some kind of home-made 3-key serial keyboard (using an encoder) for testing, and an application, which I'm making as Free Software.
My keyboard has just 3 keys, as I said, so I map them to one key (or combination) each:
Tab, Space, Shift+Tab.
This is made inside the kernel, as a module, so for applications it's just like if I had a normal keyboard, but with just 3 keys.

But I have run into trouble when trying to switch between some Radio Buttons in the same group, because Tab jumps directly outside of them, and I would need the Arrow keys to be able to select them, but that's not possible with the device attached.

My question is: is there some GTK/Gnome option from outside the application that allows to change this behaviour, so one can manage through the widgets just using three keys (they can be changed, even can be combinations of up to three keys)?? For now, I need, at least, Tab / Shift+Tab to go forward/backwards, Space for activating widgets and at least one Arrow key to switch between elements in the same group, like RadioButtons. One important thing is that it has to be intuitive, so if I use Tab for one key, I must use the opposite for the opposite key (and it's not possible to use an arrow key, because it would not be intuitive). So I cannot have Left Arrow / Space / Tab, for example.

Any ideas???

-- 
Néstor Amigo Cairo
+34 687 96 74 81
nestorac gmail com