From saddlebacking.com:
Saddlebacking: sad•dle•back•ing \?sa-d?l-?ba-ki?\ vb [fr. Saddleback Church] (2009): the phenomenon of Christian teens engaging in unprotected anal sex in order to preserve their virginities

After attending the Purity Ball, Heather and Bill saddlebacked all night because she’s saving herself for marriage.

Thank you, Dan Savage (http://www.thestranger.com/seattle/SavageLove?oid=1031968)