Shubb Partial Capo
History of third hand capo
I have found the Shubb to be the Best for the two variations of tuning mentioned. Main advantages using a Partial Capo instead of re-tuning.... less wear on strings, speed of "re-tuning", don't upset guitar shop staff, confuse guitarists at sessions :-),
But Mainly you can vary between the "open tuning" chords and standard chords, giving a greater variation of backing.
the above links may be interesting