Can non-contextual tokens be added to notification templates?

I'm a non-developer interested in modifying the default Comment Notification template:

I'm trying to figure out how to add this line at the beginning of the Notifications > Comments > Email Body:

A message from <Site Name> <Group URL>

The problem is these tokens aren't part of the Insert > Token dropdown menu.

In researching the documentation, I found this article that appears to indicate these tokens aren't available because they aren't contextually part of the template I'm editing:

Each template is a combination of rich text (HTML) and tokens. Tokens are programmatic placeholders into which contextual data related to the template being executed is placed.

For example, in a template for a notification email about a new blog post, a blog post will be contextually available (the new blog post for which the notification is being sent). Tokens related to information about the blog post (it's title, body, author, etc) are available to be placed into the template to include dynamic data related to the context of the notification to be included in the rendered template sent as the email notification.

Any guidance on how to get around this would be appreciated.

Thanks,

Justin