First, fork this gist.
From your organization's homepage (eg. https://github.com/gruntjs), open every repo's hooks admin page by running this jQuery snippet in the console, and pasting the logged output into a bash shell. It'll open a tab or two (or 27).
console.log('for i in ' + $('.public.source h3 a').map(function(){
return this.href + '/admin/hooks';
}).get().join(' ') + '; do open $i; done');
One each page, run this bookmarklet. After the form gets submitted, you should see a message in blue at the top of the page confirming that everything worked.
javascript:$.getScript('https://raw.github.com/gist/YOUR_GIST_ID/init-gh-irc-hooks.js');