I guess there's something that Schumer and Jeffries could hypothetically do, like promise that if voters help them in 2016 and 2018 with a commanding Democratic majority they will press popular progressive measures. Everybody knows there's a GOP cabal right now doing its darndest.
One such measure being expanding the Court.
Also, there's no need to let the GOP "steal Christianity" either.
(or any other religious following large enough to be a player)
But if Schumer and Jeffries are not doing that, then other possible politicians could fill the gap by promising that if supported (support seen in both issue and election polls) they will press for leadership roles. This could put pressure on Schumer and Jeffries if they want to keep their spots.
It isn't rocket science so much as willingness to fuel a known "rocket engine" in the right way.