If the Carp are ignoring bread on the surface and are taking soggy bread that is half-submerged(sub-surface) perhaps you could devise a white,fluffy marabou fly
but with the addition of some sort of parachute hackle like a Klinkhammer?Of course the hackle would have to masked as it would make the 'bread' it is imitating look nnatural,but the marabou would do this?
The marabou when wet would also have the exact texture and appearance as soggy bread?
Hope this helps,
Morgan
Edit-in case you're unsure a parachute hackle causes the hook and the body below the hackle to hang underneath the surface while the top half is above.
See this photo for an example
http://www.ledcrieff.co.uk/i/hover/klinkhammer.gif