ep_footer plugin we can inject a text (now appears on top when pad starts without formatting).
Define text here:
"ep_footer": "<a href=\"https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=N8PYR9YWQHVE8&source=url\">Pay What You Can</a> so that we can extend the board.net server capacity and stay ads-free.",
CSS and maybe even JS could be injected here as well I guess. You need to escape special characters.
Here is a simple pop-up JS: https://git.fairkom.net/fairapps/marketing/snippets/33