Callback with node ID in Quick Tabs

Question

I am planning to use Quick tabs, and it has one neat feature to use a menu as a callback and it prints the content returned from it. But How can I use the callback to pass NID so that I can return content related to that node.

Ex:

Basic Page : node/1 callback : tabs_content

Tab 1 | Tab 2 | Tab 3

function tabs_content(){
  $nid = arg(1);
  // Fetch some content related to this node
  return $content;
}

But obviously arg(1) will not have nid as this function is called from quick tabs arg(1) will be some ajax call back. So how can I get node id ? I dont want to use sessions, want to keep it clean and simple.