Add configured hidden SSID WiFi connections to the Hidden Wi-Fi Network dialog
If there is a configured WiFi connection with "hidden=true" in the [wifi] section, add it to the "Connect to Hidden Wi-Fi Network" dialog (i.e. the connection combo box), allow selecting it from the combo box and connecting to it using the already configured security information.
So far, there seems no other way to set up such connections than using nmcli.