To begin with start your game as normal and as soon as jakie appears press start to access the pause menu this will bring up the pause menu and the pause menu should appear, it looks like the pause menu.
Once you have reached the pause menu stage, leave the pause menu as it has nothing to do with this cheat.
Bang the console over your head THREE TIMES whilst singing OKI KOKI OOOOOOOOOO OKI KOKI KOKI! OOOOOOOOO OKI KOKI KOKI and thats what its all about! Rar rar!
You should now have a minor headache. This is all part of the plan.
Take your game out without turning your gba off and there you have it!!!!