Thanks so much for bumping this post Tama, I was unaware of this data for Google Analytics and it looks to be very useful.
I have been looking to implement something like this into Silverstripe itself, but If Google already does it (and better) why bother.
Okay so to get to answering the question. I was able to get data to Google Analytics by simply using "Search" as the query string.
You dont need to add the "=", just keep it simple.
Just make sure you are using Google Analytics Tracking code and you should be good to go.