I can't really well describe the hole, but if you've played Highbridge Gold then you'd know the 1,400 ft downhill hole that was to be a ball golf hole. The tournament rule was that you may not throw from on the rockpiles by the tees, but play from behind and above (higher ground). Now, imagine your drive rolls in front of the rock pile, leaning on the rocks. There is no room to get a foot or supporting point between the rocks and the edge of the disc, without marking your lie with a mini. You don't have to mark the lie because you are not O.B. or above the playing surface.
I say you have the option of playing the provisional shot because no one is sure what to do. I don't see how you can be forced to mark the lie. Playing from above and behind (on a long downhill hole it's an advantage) and marking the lie are both valid options. Can you do and play out both provisionally and take the best score since both were actually legal options.