Sidekick containers

How do I best leverage this? So I have an app stack for wordpress. I bake in the version of wordpress, and the wp-content directory that holds themes, plugins, etc is on an EFS volume. I’m trying to update plugins and themes at container start time, but that doesnt scale well having it do so before starting nginx (or I have to greatly adjust my health checks). I would like it if I could have an async container that would ignore the scale of the parent service and solely update plugins and themes. I say ignore scale as I only want one container to handle this to prevent conflicts (that cause wordpress to disable the plugin if it appears missing).