Immediately I thought of three things:
1 - Custom CSS for a community, so you could somehow add/change or maybe create a landing spot for a dom manipulation event which adds it.
In order to change the CSS, You should look at:
http://infolib.lotus.com/resources/oneui/3.0/docPublic/components/menu.htm
It's the navbar role.
In a folder such as /local/con/opt/IBM/WebSphere/AppServer/profiles/AppSrv01/installedApps/conServerCell/Communities.ear/comm.web.war/nav/common/styles/orangeTheme/
2 -
You may also want to look at /local/con/opt/IBM/WebSphere/AppServer/profiles/AppSrv01/config/cells/conServerCell/LotusConnections-config/widgets-config.xml
specifically
you could add a StackOverflow widget, when loaded it automatically opens up a new window, and transfers the person back to the previous page. ... a little bit of a kluge...
3 - Look for /local/con/opt/IBM/WebSphere/AppServer/profiles/AppSrv01/installedApps/conServerCell/Communities.ear/comm.web.war/nav/templates/page.jsp
find the line
<div class="lotusMenu" id="lotusMenu" style="display:none;" role="navigation" aria-label="Main navigation"><div class="lotusBottomCorner"><div class="lotusInner">
<div id="lotusMenuTree"></div>
</div></div></div>
You could modify the very end to add some custom link for you.
Just some quick thoughts...