Here is a clip made for another light altogether that fits the E12 just perfectly, for those of you who miss this feature. They're inexpensive, at $2.95. The only possible downside some people might find with it is that the end of the clip extends beyond the end of the light by 1mm. The light will still stand on its end, though, resting on the end of the clip and one of the flat extensions on the light. It fits fine as it comes, but I made it more perfect by slightly bending the ends of the clip inwards with a pair of needle nose pliers.
 
E12 pocket clip.