Which config file to adjust for changing the default shell for a new user?

When creating a user there is a checkbox to give user shell access.
I want to use the shell "/usr/bin/rssh", instead of "/bin/bash/"

For now I edit the passwd file manually, but i would really like the gui interface to take care of that.
Can someone help me out figuring out which source file I need to adjust?

The index.php file looks encrypted. Maybe someone can shed some light to confirm if its even possible with CWP.

Greet,
Ximperium