If anyone's interested I got the answer to this question from a consultant at an Epicor partner, Epicor themselves have not bothered to reply to my EpicWeb support ticket.
On a 64 bit Windows server the XML that comprises an Info Worker configuration resides under...
On a 64 bit Windows server the XML that comprises an Info Worker configuration resides under...
C:\Program Files (x86)\Common Files\Epicor Software Corporation\Information Worker\9.05.700\Configuration Files\Custom Configurations
... and has a unique number that matches that of the configurations ID.