Was that really worth reviving a thread that hasn't been posted in since January of 2008?
Anyway, the achievement is exactly that - an achievement. If it were easy, there would be no value to it. Anyone who actually goes through all the trouble of carrying the gnome all the way through the game is rewarded with a feeling of accomplishment, and the achievement, which is a symbol of prestige. It just wouldn't be the same if you could tuck the gnome away in a bag or stick it to the car.
I didn't make it!
You said: "At the end of the episode, when the thing is launched - you have your achievement." Thats wrong. As soon as you close the door and the gnome is inside you get the achievement. I was so glad i could finally stop carrying that ornament around!