WPMU - access site by subfolder and separate domain

I'm wondering if it's possible to run a Wordpress multisite (in subfolders) with something like domain mapping, but have the content still available though the original subfolder.



both of these display the same content, but the athletename.com has an addition of rel="canonical" to the domain.com/athletename/

That way I can have all the content on the main site, while still allowing sub-sites to promote their own URL. Sorry if this has been asked before, I took a quick look and didn't find anything.

Thanks in advance!