http://stackoverflow.com/questions/2581893/jquery-plugin-for-tinymce-callback
You can specify javascript once TinyMCE has finished loading up.
Is the oninit an option? Looking at the minified source, the oninit runs after the ajax call comeback and the init runs.
$('textarea.tinymce').tinymce({
script_url : '../js/libraries/tiny_mce/tiny_mce.js',
oninit: function() { alert("Loaded"); }
});