For those who are uncomfortable playing this game with a mouse and/or keyboard, you can use your wired Xbox 360 controller to play this game.
To make it easier to get this and the other Score achievement under original mode, you should do the following adjustments in Game Settings:
Difficulty: Level 1
Bonus Rate: Every Bonus
Bonus: 10,000 / 20,000
And if you feel you need to be even more cautious: Numbers of Players: 9
Under Button Settings (if you're using your Xbox 360 controller), I made these adjustments:
A button (Machine Gun) - Right trigger
B button (Grenades) - Left trigger
C button (Dodge/Dash) - B button
By the time I beat the game in Original Mode: I got almost 700,000 and didn't use one continue.