Your solution [clipwrap] worked just perfectly! I would only add one more thing: when copying/moving .MOV files into the 'Events' folder, it is necessary to create a sub-folder with a name for the event. This is actually quite practical, as it allows you to sort out your clips into these, well, Events. Once the files are in their proper Event folder, iMovie takes a minute or two to go through them and generate those thumbnails.
The only problematic issue remains there: performance with AVCHD. I tried this on my current generation MacBook (base model), and the most prominent feature of iMovie (ability to scrub live over video) simply doesn't work, due to the extremely heavy demands of the codec on the processor. This will be a problem with all long GOP (group-of-pictures) codecs, which is why iMovie transcodes video into AIC by default. Situation is somewhat better on a new iMac (Core i3), in that playback is smoother, but scrubbing most definitely won't work as expected. You still get a lot of spinning beach balls. If you can work around the scrubbing feature (mousing around carefully, to avoid swiping your mouse pointer across a video clip), you won't see that beach ball that much.
The advantages of the editing of AVCHD directly are (at least) two (that I can think of):
1. Reducing/eliminating any artifacts that may be introduced during transcoding from AVCHD into AIC;
2. Conserving hard drive space while editing (AIC would take up to five times as much space)