Does Tyler Sash count? He beat out a returning fifth year starter in Harold Dalton. Wasn't so much next man in...as he was freakishly good (and Dalton was bad).
I think Joe Conklin is a severely underrated next man in story. Local kid who walked on at Iowa State, realized it sucked. Transfered to Iowa and was on the team for three years. Because of transfers and lack of safety depth he made the 2-deeps out of nowhere his senior year. Greenwood gets injured against MSU, Bam, Conklin is the starting FS on a top 10 team. And since he didn't blow any coverage or make any other epic mistake in his three games, his play passes as serviceable.