I know this achievement can be very stressful, so my video will help give you an idea of how to do it... As I got this achievement earlier today. This will require a bit of luck, determination and trial and error.
I did this on stage 1 as one of the rocks is pretty high up making it easier to hit four with one rock, so you can get that 4 enemies achievement
as well. It's kind of hard for me to explain how to do this, which is why I urge you to watch my video and see how I did it:
Hopefully my video helps!!
P.S At the end I show you my failed attempt so I hope seeing that motivates you to do well.