Avoid `blog` in frontmatter

I have a source/atom.xml.builder file I am using to generate a feed from the 2 blogs I have setup.
It merges both, so I use a custom method to list all entries, though, the blog extension forces me add
blog: blog_name in that file frontmatter or it error out, but it does not belong to either one.

How can I avoid having to add this?

Did you ever find out the answer to this?