How to install a FB Ad Pixel in Header.php so it acts on the whole site

I have FB Ads working in the site, and I have a pixel to go in the header of every page including the home page. Do you know of a way of making it sit inside header.php other than programmatically adding it in every time the theme upgrades?

I haven't been able to find one.
I have a plugin to put the pixel on individual pages - which is necessarily for other purposes, but that doesn't work on the Home page of course.

Any thoughts would be appreciated.
Cheers - JC