Putting yourself in a situation where it’s Misasek? People have all sorts of idiosyncrocies and compulsions, as well as unconscious habits. That’s what the Halachic category of Misasek is. If not biting your nails then someone will have a different one. It’s very different than making a conscious choice to put yourself in an Oneis on Shabbos.
On a slightly related note, I once heard someone say that he avoids doing a certain action on weekdays so that he won’t do it on Shabbos. I said, “That’s very nice, but I think you’ve missed the point of what Shabbos is.” Have you ever thought that it’s weird that we have no G’zeiros Chol Atu Shabbos? It’s because (in my opinion) when you turn weekdays into Shabbos, you defeat the purpose of Shabbos.