Walter B. Gibson seems to be the first to have published a rising card effect using the Plunger Principle. This appears as “The Simplex Rising Cards” in Gibson’s “Practical Card Tricks” column in Dr. J. E. Pierce's The Magic World, Vol. 7 No. 9, Jan. 1924, p. 124. The chosen card is forced into the deck in a manner that causes the surrounding cards to jut out the inner end. These are then pushed upward and flush to cause the selection to rise. Gibson considered this a novelty rather than “a finished effect”. (Thanks to David Britland for discovering this reference.) It did not make the cut for Gibson's earlier booklet of the same title, Practical Card Tricks, 1921, or its three sequels (1926-28).
Seven years later, Lawrence Kam published a similar card rise using the plunger principle, calling it “Priceless Card Rise” in The Seven Circles, Vol. 1 No. 6, Sep. 1931, p. 8. However, William Larsen Sr. defended Jack McMillen as the inventor. When Larsen published the “McMillen-Wright Rising Cards” in Genii, Vol. 1 No. 1, Sep. 1936, p. 9 (also see McMillen's “Obedient Rising Cards,” p. 10), he stated that McMillen had shown the plunger card rise to him and T. Page Wright “as early as 1928.” Larsen admits showing the idea to William McCaffrey and Howard Van Brunt (who performed it) after Wright's death in December 1930, and suggests that this led to its publication by others. He specifically mentions Burling Hull (Hull didn't claim the principle, only handlings of it), who in 1935 published versions in Stage Magic, No. 2, p. 3, “An Unique Sleight of Hand Rising Card”; and No. 3, p. 79, “The Spirit of Little Bo-Peep (Jumbo Cards)”.
However, the Gibson entry, although the handling is rather crude, precedes Larsen's claim for McMillen's invention of the idea. McMillen would have been just twelve years old at the time, and living in California, while Gibson was in New York City.
As an aside, it appears as though Edwin Sachs knew of the concept without being aware of its potential. In Sleight of Hand, 1877, p. 98, as part of the Diagonal Pass description, Sachs advises against pushing the cards through the deck injogged because “the act of pushing them down is extremely likely to carry along with them indifferent cards intervening between two of them.” So while Sachs seems to be the first to describe the principle in action, it was as a cautionary tale rather than as a method to pursue.