The quest "Now This is Ram Racing... Almost." should automatically mount the PC on a ram. The quest doesn't do this and there doesn't appear to be any way to do this. This video shows what should happen (this is from a later expansion but as far as I know, the quest works the same way). It looks like the quest is supposed to auto-cast this spell on you and then this spell on completion; the first auto-mounts the ram, the second dismounts it.
(Not shown in the attached video, but I also tried using the item directly from the bag instead of the quest tracker; didn't make a difference)
Quest ID 11318, reported 10/10/2018, MaNGOS Two test server Covenant - Solar Flare.