The Imitation Spice Girl Song is sung by Roger when the family becomes lost in the desert in "There Will Be Bad Blood". Roger comments that the area looks just like a place in a Spice Girls video and starts to sing, admitting what he is singing isn't really one of their songs.
Roger: Give it up, girl
You get it, got it
You can do it if you really want it!
That-that's not really one of their songs
But it's-it's crappy like that.