Sorry to get back after a while but just wanted to check the activity on this thread. Do we have any alternate solution ?
If the only option is to go down the route of overriding footer() function in custom theme, then it raises another question for me - How to determine which theme to override?
Meaning if we need to install our block plugin across different Moodle installs that are already using their own custom theme then how do we create a plugin that has our
--- custom block functionality
--- AND custom theme_overridden_renderer_factory within that determines the current "theme" (standard OR custom) to override footer()?
I'm hopeful to find an answer to this as I'm sure this could solve the problem for lots of people with similar issue.