wow.... we've really hijacked this thread, guys!
i use the TAP ISO pickup (from Greece). i've got a bunch of them, and have become pretty fearless about the drilling and tapping routine to install their pickup adapter. the adapter allows you to unscrew the pickup itself, and replace it with a threaded plug, for when you're playing acoustic.
it really doesn't make much difference in the acoustic performance characteristics, and the sound is excellent. also, of course, the drilled-in types give way better isolation and immunity from feedback. there's no way i could be functional in a lot of my loud performance environments without this kind of pickup!
i've drilled into barrels on clarinet, as well as mouthpieces for saxophone. for bass clarinet, i'd probably drill the neck and solder on a threaded brass nut (or tapped brass block if you wish to be fancier!) -- this is how i've got my contralto clarinet set up. on the other hand, i'm sure drilling into the mouthpiece would work too -- i've done that on my baritone saxophone and it works great! the only fussy thing about doing it on a mouthpiece is that you have to find a way to co-exist with whatever ligature you're using. i've modified my ligatures to provide a pickup-sized hole, so the pickup can protrude out through the lig.
~~~we totally need to re-name this thread "woodwind nerd-talk"~~~