You could create a plugin using the "global_setup_complete" hook and modify the $footer variable at that point (you'd need php code to read in the file, which I guess could get complicated if it includes styles or javascript) Of course you could just copy the HTML you want to the footer template, but I guess if that would work for you you'd have done it already.
the data in the .html file is updated every 5 minutes so that wont work.