I've been trying to get my head around these keyboard layout files and I think I get the basics but I can't achieve my goal.

Basically what I'd like to do is to disable that virtual symbol keyboard which is popping up on the screen when pressing Fn->Ctrl and map some of these symbols as fourth level of the hardware keyboard. For example Fn->Ctrl->J would give ] symbol. I'm looking at English hardware layout where J has ) as 3rd level, so it makes sense to assign ] as 4th level.

I also need Polish characters directly on hardware keyboard rather than virtual one (it's huge inconvenience), so I'd like to be able press combinations like Fn->Ctrl->A = ą or Shift->Fn->Ctrl->A = Ą etc.

I managed to disable symbol pad appearing, but I don't know how set Ctrl key to bump up a level *after* pressing Fn (which switches 3rd level by default, obviously). I tried trick with assigning dead_caron character to 3rd level of Ctrl key as suggested by Mitja earlier but it didn't behave as expected.

Any feedback on this will be much appreciated, as typing in Polish on N900 is currently a horrible experience and I'm desperate to change it.