What Felber is suggesting in his paper, IMHO, is that instead of 'thrust' propulsion (as we presently use it to 'blast off' or through space) we might be able to accelerate a massive payload through space by trailing behind a high-speed particle moving near c, essentially being sucked through space at ever-increasing velocities (without gravitational stress to the massive payload) by the leading particle's anti-gravitational field seen to exist by Felber's exact calculation of the Swartzchild solution to Einstein's equation at speeds greater than 57.7% of c.
Still, as General Yeager said, "Spam in a can..."