Rasta,
Those partial capos like Third Hand or the Drop D Kyser are absolutely fascinating to me because, unlike altering the tuning (for instance drop D), you haven't changed pitch by tension but by string length. Thus, if you "fake" drop D's relative pitch by partially capoing A,D,G,B,&E and leaving the low E open, you can still play your G (now an A) as you normally would, as well as all the barre chords.
leeneia,
When I'm playing in drop D I still sound the E in my E & Em by merely reaching up above the B I'm already holding down and hold down the E (now at the second fret)(critical for playing "Castles In The Air"-D.McClean). The C doesn't need the low G to be a C chord but if you want that fuller sound, depress the G (now a the 5th fret) and the C chord will be right there below it on the D,G,&B strings--purdy handy huh? As for the A...are you pretty handy at thumbing over? You can hold down the E with your thumb, though again, it's not necessary to the chord.