I've had a few friends that have made it to the top at least once, so I got some information from them on how to do. Apparently you have to sneak around the back side of a temple, cross west and run into the trail out of sight of the guard. So that is what we tried. After wandering around a dozen or so graves and cattle trails, we finally made it back to the temple. On the far side of the temple we thought we found the trail head, and began hiking in stealth mode. The trail continued through a monument/grave area and then into the thick underbrush.
The view from Sanbansan was pretty amazing. I wish we had more time to explore, but I'm happy that I can finally say that I climbed the iconic mountain.