That tip from sophocleese is a good one. I use two Shubb capos for that very purpose. One is stock, the other is sawn-off so that it only frets five strings. That way you can get the drop-E effect in other keys as well. The problem with fretting five strings with a standard Shubb is that it tends to pivot on one bearing point at the back of the neck, which can have disastrous consequences in the middle of a song. maybe Kysers work better for this purpose?