I am not sure that is possible with this internal SFDC function. As mentioned in this topic (The Service Cloud Console – Working with Buttons and Links):
when opening Salesforce.com pages, the tab title is set automatically.
and
when opening Visualforce pages, the Visualforce page is responsible
for setting its tab title.
But... Why not using a native service cloud console integration API? It is working well for me:
{!REQUIRESCRIPT("/support/console/30.0/integration.js")}
// Use the results primary tab id and open a new subtab
var openSubtab = function(result){
sforce.console.openSubtab(result.id, 'your page url', true, 'page title', null);
};
sforce.console.getEnclosingPrimaryTabId(openSubtab);