I think that might work. I may test that today some time. In fact the 7940/7960 (if you open the face plate) is exactly the same h/w. Just that the front buttons on the face plate show up as 2 on the 7940, even though there is provision for 6 buttons.
PS: note that you may not call Cisco for support as this will be an unsupported config.
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.