This isn't a fetish, I think he's run out of feelings. When you spend every waking moment pinned ; and I mean really pinned, $1000-a-day pinned, as pinned as this guy's health issues force him to be to avoid crippling unbearable pain, pretty much everything you ever feel is muffled and barely even there. You can't feel happy, you can't feel sad, you can't feel horny, you can't feel fulfilled, you even start to miss basic bodily demands like hunger and thirst. Eventually you begin to crave emotions so badly you don't even care what they are anymore, as long as they're emotions.
When every other feeling is so far gone you don't even remember what they were like, guilt and shame are the last things you're able to force yourself to feel, and I think that's where Frederick is at now.