If I understand your question, it seems you want the button to be in the tabBar itself, and not in its own toobar? If this is the case, you can use the following code available in this script.
http://jsfiddle.net/Sadnj/15/
Ext.create('Ext.panel.Panel', { renderTo: Ext.getBody(), id: 'testPanel', height: 200, width: 200, items: [{ xtype: 'tabpanel', activeTab: 1, tabBar: { items: [{ xtype: 'tbfill' }, { xtype: 'button', text: 'Test Button' }] }, items: [{ title: 'tab1', }, { title: 'tab2', }] }] });
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