Yes, I agree that could work.
I had thought you meant to wait until there was already an overpopulation, with mature females and males, and separate them then (at which point the mature females are going to keep pumping out babies anyway.)
Separating them does not make much difference with guppies. Female guppies store sperm even better than female chickens.
As a practical matter, assume that if a female guppy has EVER bred with a male, that she will keep having one batch of babies after another for her entire life. And if it...