There was a story in the early days of the internet (maybe 1995 or so?) on one of those alt.sex.bondage forums (not tickling per say, but oh was there tickling) of a chick who was tied up by her boyfriend, telling the story in first person, about how he had her kneel naked on a chair, facing backwards, so that her feet were hanging off, soles pointed behind her, and she was gagged, and she was comfortable but there were nipple clamps and other things. Anyway he does some bondage stuff to her, spanking, nipple stuff, etc. Then he leaves for like 30 minutes to let her stew there and think about what he's going to do to her. And he comes back and she feel him painting some stuff on her soles with a brush, sweet slippery food of some sort, and she's screaming through her gag because the brush tickles so bad. And then the boyfriend whistles and she hears their golden retriever scamper into the room, and her eyes bulge and she starts REALLY screaming because she realizes what's about to happen, and low and behold the dog goes to town on her feet, licking them clean, up and down her soles, between her toes, driving her completely bonkers and she describes it as the most ticklish feeling she's ever felt in her life, like being electrocuted but in a pleasurable way because it was so intense, and she eventually comes, just from the dog licking her soles. OH MAN it was so hot. And it seemed completely true, it wasn't written in some fantasy way. I think it might have even been the answer to a bulletin board question "What's the most intense bondage thing that you've ever experienced?" or something like that.
Does this ring a bell with any old timers? If not maybe I'll try to re-write it from memory, lol.