I have never done it but for something like this where the stripes are un-even, I would start by putting on one pre-cut stripe then cutting 1 straight line on another piece of fondant and laying it next to the existing stripe. Then use a ruler and scalpel to cut the new piece to the required width on the cake itself and remove the excess. Then repeat all the way around the cake until they meet. I can't think of any other way of taking into account the changing widths that would be required for each piece otherwise without having to do lots and lots of maths! I guess it would help in terms of keeping the lines nice and straight as well.
As i said though, I have never done it so if there is a better way, I would be eager to know as well! I think that the guys at Planet Cake in Australia do quite a few cakes with this effect on them...maybe it has featured on one of their TV shows at some point??