Hello,
You can accomplish it by adding the below mentioned parameter to jabber-config.xml file. If your CUCM version is 12 and above, you can build that file from within the CUCM. Alternatively if you've one already, just add it under Options section.
<DockedWindowVisible>false</DockedWindowVisible>
DockedWindowVisible
Applies to Cisco Jabber for Windows.
Specifies if the docked window displays when the client starts.
• true (default)—The docked window displays when the client starts.
• false—The docked window does not display when the client starts.
Example: <DockedWindowVisible>false</DockedWindowVisible>
-Sankar