The one time I can recall this is 1995 Northern Illinois at Florida when Spurrier sat Danny Wuerffel.
From Wikipedia:
"At homecoming the following week, backup quarterback Eric Kresser played in place of Wuerffel for the Northern Illinois game, a 58–20 defeat of the Huskies. Kresser threw for a school record 458 yards, breaking the record Terry Dean set against Southwestern Louisiana in 1993. Kresser passed for six touchdowns to six different players, including a 96-yard pass to Jacquez Green on a crossing route.
Despite the performance, Spurrier felt Kresser threw better in pre-game warmups. The Gators improved to 8-0 for the first time since 1928."
And now you know
Edit: I think Iowa State started their 2nd- or 3rd-string QB against us on Senior Day in 1992 and beat us 19-10.