This can be done using any maze but you have the best chances if you play on the Expert difficulty. Strategize your moves so that you have a long trail of ghosts to chase you. Remember, eating a fruit at one side removes the ghosts on the opposite side of the maze. Thus, you will want to wake them up before grabbing the fruit. When the power pellet shows up (not the one that you start with) eat it and take out all the ghosts and build your trail again. Save that starting power pellet for when the time begins to run out. Eating the long trails of ghosts will contribute a lot to your score. This, the fruits and the Pac dots should get you past the 500,000 mark which will get you the achievement.