add tinymce plugin via wordpress plugin.php

function wpaInitTinymce() {
	// Add only in Rich Editor mode
	if ( get_user_option('rich_editing') == 'true') {
	// add the plugin for wp25 in a new way
		add_filter("mce_external_plugins", "wpaAddTinymcePlugin", 5);
	}
}

// Load the TinyMCE plugin : editor_plugin.js (wp2.5)
function wpaAddTinymcePlugin($plugin_array) {
	$plugin_array['wp_audio'] = WPA_URL . '/editor_plugin.js';	
	return $plugin_array;
}

// init process for adding plugin
add_action('init', 'wpaInitTinymce');