Hello,
How can I make the incoming call screen portrait mode only?

I got the latest CSSU, there is the portrait mode option but its not what I want.

I want to make the incoming call screen (only this screen) always stay in portrait mode and never even try to switch itself into portrait while in call.

The reason is:
When I get call, I pick my phone from my pocket for example, and I hold it in portrait mode, but then instead of showing the buttons they disappear then its try to make it landscape mode then it decide to leave it as portrait and when I want to hit the closest wall with that N900 its finally set.
because of this funny thing I hit 'reject' like 30% of the time
Its freaking me out! My phone is lucky I don't get too much calls per day so its still in one piece.

Please help me, I don't familiar with the system source code. (I only managed to add the restart button).
any guide or something will help.

Thanks!