I have some great photos taken along the highline, courtesy of a D&SNG photo charter. The train would stop and let the photographers climb up the cliffs, then do multiple runpasts. This is the only legal and safe way to do it, with a radio equipped railroad employee in the photo line, directing the train movement.
You also get a much better looking train, although we did shoot one of the regular trains too, when our special backed into the clear for the meet at Rockwood, while we were still up on the cliffs.
Photo trips are organized by a number of groups, as well as the D&SNG themselves. Try it, you'll like it.