The rocket is found well before the end of the game, so it’s only a few hours of play anyway.

If you know the game (I assume everyone will have played through this episode at least once before trying this achievement!), you’ll know which rooms you’ll be coming back to, so you can leave him for large sections of the game.

There are a lot of battles where you can just set him down somewhere until after the fight. This actually isn’t as hard as you might think. I had already beaten Episode 2 on the PC, but we just got it for the 360, so I wanted to play through it again anyway (points!). When I first read about the gnome achievement, I knew I had to do it (partly because it sounded fun, partly because I love Amelie).