I'm unaware of any css solution that could work for this case. The thead would repeat the element on the top of every page for you, but I'm afraid you won't be able to position it as you want.
I'm afraid you will need to stick with the pdf utils merge. To optimize rendering, you can render the chart just once and merge it to all pages using jsreport script
https://playground.jsreport.net/w/anon/1RyVSTCV
Maybe you can use it as a "component" and append/prepend such template to other templates again using pdf utils and scripts.