Yep, what Irulan posted! DH made a rack for the interior of our Element that held four bikes (back/front/back/front) with the fork mount brackets. He also made one for the back of his truck when we had a tandem.

Barring that, I have used a few bungee cords to keep one bike upright without removing the wheel in the back of the Element (when we didn't have the rack with fork-mount thingies). You just wind the bungees around various parts of the bike and then around various parts of the interior of your car. Takes a little experimenting to get right.