Can I mod rewrite to a different document root?

Solution 1:

For files outside the DocumentRoot, check out the aptly named documentation section on "Files Outside the DocumentRoot" -- you're looking at creating an Alias, and you may be able to do it without a redirect.

Solution 2:

RewriteCond %{DOCUMENT_ROOT}$1 !-f
RewriteRule (.*) /var/www/shared$1 [last]