I think the best you'll get is one of the cases with a wrist strap (the 4gamer one I have had a wrist strap in for case but I never used it, and the DS Lite is held in the case by 2 strips of elastic which I don't use either though)
Never felt the need for one though sat somewhere using it.
The old DS wrist strap had a thumb pad for those scrolling games rather the select type you use the stylis for, plus if its on my wrist i can use my hand for other things, like i do with the wrist strap i use on my camera
Sat somewhere you dont need but on the move you do, plus if someone trys to nick if from you on the train, they'll get your arm as well
Setting aside all of the suggestions of masturbation, does anyone know where you can buy a better wrist strap for the DS, or maybe even a plastic thimble type thing to go on your thumb? The basic one is crap...