I have been tripping over this for days and finally, though the miracle of this thing called Google, found a mailing list post describing exactly how to do it. Here it is, relinked so that others may find it.

Don’t you ever feel really dumb when you realize that what you’ve been trying to do for days is actually so easy? I haven’t worked as a sysadmin for 4 years now and find my skills have really atrophied… but anyway… thanks to the Google gods I have managed once more to get away with it.