I agree, the clip is mounted all wrong. It's quite impractical. With the way it's positioned, over 1/3 of the light sits above your pocket...and it's the lens end at that! If it was reversed and mounted near the tail end, it would sit much lower in the pocket...and the lens would be better protected by facing down.
Those screws take a #5 Torx driver...which can be a little tough to find...(Sears Torx drivers start at #6, unless you can find them in a set). A good electronics store will have them.
I measured as best I could using calipers and it looks to me like the holes have been drilled and tapped not much deeper than a 1/16". All you need is enough to grab a few threads. I'm not even remotely knowledgeable enough yet about these lights to want to risk taking apart the tail assembly, but it seems to me there'd be enough thickness in that somewhat wider "ring" about 1/4" down from the tail, to drill and tap.
I would think that there's someone out there who's taken these apart and could advise if that area is thick enough to accomodate the screws.