Adding no-index to sitemap

Unusual question here…

I use a custom plugin to promote sub-blog posts to my main blog. This way, my main blog can aggregate sub-blog content. It’s similar to sitewide tags.

The problem I have is that these sub-blog posts are showing up in my sitemap with the sub-blog permalink, and Google is rejecting my sitemap saying “URL not allowed”.

Is there a way for me to automatically add a “no-index” attribute, in the sitemap code, to any content with a subdirectory permalink?

And, would this solve my problem?