I would tend to ignore the fact that there is a Technic cross hole in the light switch. I guess it may be handy in some cases, but frankly it seems easier to me to just push the button with a lever or cam.
To do that, the best part is probably the Technic Cam, possibly two of them side by side. Don't drive it through the center hole but through the one just next to it, that is, the middle one of the three adjacent ones.
Positioning it so that it pushes the switch shouldn't be an issue, but of course you'll also have to motorize it somehow. I guess the easiest would be the new servo motor but you'll need to wait for it to be available separately (should happen during 2013), and of course it takes some space. (If you want to be creative with precision positioning, you could use an old 12v train switch remote too, I guess).
Of course, any motor will probably do, but then you'll have to make sure it doesn't turn too fast or it's going to be tricky to hope it stops in the desired position.
Another wacky idea would involve a wormscrew right on a rack, which would slide in or out of position, but I'm not sure it would be that easy. And if you're willing to go that route, a simple actuator is probably easier.