Are you redirecting via your
public_html/.htaccess file? If so, you should be able to adjust it so that
only mydomain.com (with or without www., with or without trailing slash (/)) is redirected, while everything else stays at home. Is that what you're looking for? It may be as simple as
RewriteEngine On
RewriteRule ^$ http://xxxxx.wordpress.com [R=301]
That
should say that if you give no explicit directory path or file, your visitor will be redirected to wordpress.com.