as long as nothing is overfed, you are fine. Flushing is not a required step and doesn't have a measurable effect anyone can prove, so far. If your heat is set on it, you can still do it and it also won't cause any problems. It's in the same boat as mass defoliation just for the sake of defoliation.
Looks like hobbit has the best idea, but if no shutoff available, go ahead and top off with some plain water for the plant that is ahead of schedule. The extra runoff will dilute the rootzone and accomplish the same thing.