Sorry for the late response.
You would follow the much the same steps as the example under ‘Permanent Redirection’ as the 301 HTTPD status code is very important for search engines as Google. I haven’t tested this code but it should work.
<rule enabled="true">
<name>Permanent blog example</name>
<condition name="host" operator="equal">www.mydomain.com</condition>
<from>^/blog/(.*)$</from>
<to type="permanent-redirect" last="true">http://blog.mydomain.com/$1</to>
</rule>