In the "Configuring Apache" section, the Configuration Guide mentions:
"Now, either create a VirtualHost entry (to put Phabricator on a subdomain) or edit the Directory entry for the DocumentRoot."
However, the mod_rewrite config below doesn't actually work in a <Directory> block (at the very least, it doesn't seem to work in a Directory block outside a VirtualHost), since the RewriteRule will match against the filesystem path, not the request URI. See here:
http://httpd.apache.org/docs/2.2/mod/mod_rewrite.html#rewriterule