We'll create fresh WordPress site with Sitewide (Admin) Header/Footer installed. You have 20 minutes to test the plugin after that site we'll be deleted.
This plugin allows you to add your code/text to the headers and footers on all the blogs in the blog network and in the backend of all blogs too.
In addition, it is possible to replace the footer bar text in the backend completely.
You can access the settings under Network Admin -> Settings.