The widgets code has been released for public consumption as a WordPress plugin and appears to work out of the box for WordPress MU. However, this would still require a user to ‘activate’ the plugin before use as opposed to on wordpress.com where the plugin is enabled site-wide. This is relatively simple to achieve and involves the following steps:
- Copy the widgets directory and everything in it to /wp-inst/wp-content/mu-plugins/.
- Download widgets.txt, rename it to widgets.php, and copy it to /wp-inst/wp-content/mu-plugins/ (not in the widgets directory).