You have to create a temporary wifi network on your mac (imac, macbook, mini) where your BIAB files are.
see an example:
http://beatsurfing.net/connect-mac-wifi/

step 1: create a temporary network on teh mac
http://beatsurfing.net/wp-content/uploads/2012/06/01-create-adhoc.png
http://beatsurfing.net/wp-content/uploads/2012/06/02-create-adhoc.png
http://beatsurfing.net/wp-content/uploads/2012/06/03-create-adhoc.png

step 2: connect the ipad to the new tempoary network
http://beatsurfing.net/wp-content/uploads/2012/06/04-create-adhoc.png
now you get in the BIAB ipad app, the ip address you have to use in the browser on the mac.