Score based on time?

Hi all. I have a score actor set up in my scene displayed at 0 but all the tutorials I've seen so far need some interaction to be made with an actor (Like blowing up) to advance the score. What I'm trying to do is have the score increase the longer you survive in the game. So from when it starts to game over the score would run up and stop at game over. Also if its possible to be able to double the amount of the score every 30 seconds. Is this possible?
Comments
timer:
every 1 seconds
change attribute: game.score to game.score+self.addition
timer:
every 30 seconds
change attribute: self.addition to self.addition*2
http://img59.imageshack.us/img59/9819/screenshot20110322at164.png