The word backflowing is playable in Words With Friends™, no blanks required. Because it is longer than 7 letters, you would have to play off an existing word or do it in several moves.
Words With Friends™ Letter Score: 31
Highest Scoring Words With Friends™ Play In The Letters
Seven Letter Word Alert: (24 words)
backing, backlog, balking, bawling, bifocal, blowing, bowling, cabling, clawing, coaking, coalbin, coaling, cowling, flaking, flawing, flowing, foaling, fogbank, gablock, lacking, loafing, locking, walking, wolfing