Why would you want to turn it off during a dive? Leave it on until you are back at the surface. Are you trying to save batteries? I use alkaline batteries in my backup but have rarely used it, so cost is not something I personally worry about. I have given it to other divers, since everyone having a light helps keep track of dive buddies on bad vis days. For us a light is a tool for signaling and marking our position.
I was asking purely from a drill standpoint. I hadn't really practiced one-handed stowing because I didn't really see any reason it would come up. When doing drills, I've needed both hands to get it through the innertube, so if it was commonly done with one hand, I'd switch just to figure it out.