I always find an ordinary capo will work fine for just fretting the top five strings.

I've thought of getting one of those tuning capos, but I've felt it'd be a bit of a drag trying to work out what was what, with six strings all liable to be different.

One idea that's always struck me as handy is the banjo 5th string capo idea, and I wonder if anyone's ever used one on a guitar. (Or the little hooks banjo players use for the same purpose.)