Way to add Google Tag Manager code to WP admin areas of Multisite Network sites?


I would like to add a chat widget to my network, so my site owners can chat with me and my team (the network admins) to get support.

I have found some software that looks like it might work at: http://www.socialintents.com/live-chat.html But I'm not sure how I can install the script so that it'll appear in all the sub sites admin areas...

I was wondering if you could help me with a bit of code that can add it in via an mu-plugin or something... (or whatever you think is best).

I was thinking of using Google Tag manager to manage this script (and possibly other scripts)... which has two placements, one in the <head> and one immediately after the <body> tag.