Lix: Ok it looks like everyone feels you can not replace it without replacing the entire top. Since you have the part already, just look at it and see where the part has mounting points and work it out in your head how it should come apart. The worse you could do is damage the top and everyone above feels you will have to replace it anyway so what do you have to loose.
I it were me I would have a heat gun and the top panel and go to town. But make sure you can get the replacement keyboard top if it does not go as you expect. Do Not Use Metal Tools to pry out the mouse pad as you will scratch the paint on the top board at the very least.
Look at it and give it a try but be slow and watch what you do.
good Luck