In reply to benmason:
If your anchor points are only 2ft apart
and you are looking for a BACKUP ... i.e. not load bearing while people are climbing .. only in the case of a system failure
then.....
I would suggest
a long steel chain linking along the whole line of screw gates
then most anchors will have two backups
the end points - worst case - one back with a max fall of 2ft (still way better than no backup)
IF you are concerned about the chain being on the same screw gate that the rope runs through
THEN ... add another screw gate to each hanger .... so your rope will run one screw gate lower
or you could use maillon to link chain/anchor/screw gate
.... just an idea .....