Caching/storing hostname mapping?

[graq]

I have some nginx configs that sometimes host mutiple domains and some
file requests are mapped to the disk using some language.

And example would be WordPress MultiSite. Where
blog1.example.com/files/file1.jpg makes to blogs.dir/1/file1.jpg and
someanotherblog3.example.com/files/file2.jpg maps to
blogs.dir/45/file2.jpg 

These could be rewritting by hand individually to allow nginx to
naturally cache the file, rather than handing it over to WordPress (PHP)
map and server back to nginx.

Is there a way I can programmatically build these?

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,182305,182305#msg-182305