Although functionally the same, there were a couple of different chain carrier gadgets shown in one Campagnolo supplement published around 1977. Here is that page as well as the one showing the shift lever with the small additional tab which certainly does look as if it could be easily pressed into service - unintentionally.
http://www.flickr.com/
Apparently these were poor selling devices. The hangers (but not shift levers) appear again in a 1982 Campagnolo publication, but were never mentioned again.
I have one bike which included two threaded holes at the inside of the forged Campagnolo 1010/B dropout for attaching the 2-screw version of the carrier. The bike was made in Italy by Gianni Motta during the late 1970s.
http://www.flickr.com/
The innovation must have been initially promoted as the very latest clever racing accessory from Campagnolo... but all the flaws in the concept mentioned by others seem to have quickly doomed the devices to a very brief production period.
A 1957 Rene Herse Randonneuse which sold at auction on eBay had a similar device built into the bikes rear dropout:
http://www.flickr.com/
Perhaps that was a better use for such an accessory than bolting one onto a production racing bike... 20 years later?
BOB HANSON, ALBUQUERQUE, NEW MEXICO, USA