Way to update offline installations

Currently updates are only available for online installers.

Qt users would be interested in feature to update installations done via offline installer.
Here is one description of wanted features from a user:
"
*
create an installer that can act as updater also,
*
So, if the installer starts and recognize the application is already installed,
should switch to updater,
*
our target PC usually have NO internet connection, so I cannot use online repository
*
the updater should override only target files and should take configuration files as they was
before updating,
"