Looking for the Source of a Teaching on Sexual Ethics from Benedict XVI or JP2

Years ago, I recall being taught that Benedict XVI once said that it was licit for a husband to perform cunnilingus on his wife in order to help her climax if she did not during the ordinary process of the marital act. My memory could be fuzzy, and perhaps it was JP2 who said this (would make sense, given his large contribution to catholic sexual ethics), but I'm 90% certain that I was told it was Benedict XVI. I would like to know what the source is for this claim, however, and I have been unsuccesful when searching for it in the past online.