All the more reason to have two 11 episode seasons (Fall and Spring), rather than one 22 episode season stretched out over the same period. (Or half seasons).
And another trick they could use, the same one I advocated instead of cancelling Green Lantern and Young Justice (oh I'm sorry, putting on indefinite hiatus, they haven't actually been cancelled) for Beware the Batman and Teen Titans Go. Same trick ABC uses for Agents of SHIELD, while it is off, put another genre show in the same slot - keeping the target audience for every week.
Say, Legends of Tomorrow as a fill in for Flash, and Vixen (or Constantine, or whatever) for Arrow.