To use this code, first go on your active bundle page, and open a JavaScript console. On Firefox, it's Ctrl-Shift-K, while on Chrome it's Ctrl-Shift-J. Then paste in this line:
addChatTab=function(b,d,g){for(var a=Object.keys(chatBoxer.chats),c,e=0;e<a.length;++e){var f=chatBoxer.chats[a[e]];if("common"===f.type){c=f.el;break}}a=c.clone();c=c.prev().clone();c.attr("data-chat-id",b);c.find(".caption").html(g);a.attr("id","chat-"+b);a.attr("class","chat");a.attr("data-channel","/bundles/"+d);a.attr("data-id",b);a.find("form").attr("action","/chats/"+b+"/messages");a.find(".log").empty();d=c.prop("outerHTML")+"\n"+a.prop("outerHTML");chatBoxer.addPrivateChat(d);b=chatBoxer.chats[b];b.type="custom";b.subscribe();b.type="common";return d};
and press Enter. Next, go to the bundle you want to copy the chat tab from, and open a JavaScript console. Enter this:
(function(){var a=$(".chat.currentPage"),b=a.data("id"),c=a.data("channel").replace("/bundles/",""),a=a.prev().find(".caption").html();return"addChatTab("+b+", "+c+", '"+a+"');"})();
The console will display the command you need to type in the first (active bundle) page. Do that, and the chat from the bundle you wanted to copy from will appear as a tab in your chat box.