Stephen Minch details the history of this flourish in The Collected Works of Alex Elmsley, Vol. II, 1994, p. 13. Elmsley was the first to roll down cards into position like coin and billiard ball manipulators before him, but the practice of holding cards in the final position dates back to the early 1900s. Reinhard Müller found a photo of Servais Le Roy posing with the cards already in position. Elmsley was directly inspired by Hans Trixter's “Manipulated Four Aces” from Abra, Vol. 6 No. 139, Sep. 25 1948, p. 131. Trixter would produce the aces with one hand and then transfer them into the final position in his other hand.
A related idea is “Finger Stand” in Ben Berger's Highlight Magic, 1941, p. 20. This isn't a roll-down, but the cards are placed between the fingers for display.