I've read about this (reversing the lens) and it is possible. I've never tried it - don't have the patience or the time. You'll have a razor thin depth of field, but assuming you are persistent and patient, it will work. I'd buy the adaptor ring as opposed to drilling my own lens cap - you'll likely want to replace the cap if you ever resell as opposed to try and explain to the potential buyer what is up. I would highly suggest using a tripod and self-timer/remote while doing this, otherwise you won't get a sharp image due to shake and the very narrow depth of field.
The extension tubes are another way to go, never tried those either, but considered before getting a macro lens. I think I would pick up these first before trying lens reversal. If anyone attempts it, please post some pics! ;D
