*scratches head* From what I recall 7 stringers have an extra low B string tuned to standard - and a correspondingly wider neck- so i guess that for chords you can use the 7th string instead of the 2nd, or if you have enough fingers play at the same frets on 2nd AND 7th!

The whole idea of 7 [or 4:)] stringers is a bit weird for me (although I have never played one) ,because if you need pickups/parts to upgrade a 6 string they are widely available..but for a 7? -besides look at all the fantasic (tecnical as well as feeling) music that has been made with 6 stringers. [ok,ok AND with basses as well].