You cannot use the “Press this…” function directly in Reader as it is Javascript and Reader wants a URL. But, you can just post directly to press-this.php. The URL is (make sure to replace with your own domain name!)

http://www.YOURDOMAINHERE.com/wp-admin/press-this.php?u=$url&t=$title&s=$source&v=2

Google Reader will substitute the items in braces. Now you have an easy “Send to…” option from Google Reader.

via Using Google Reader “Send To” with WordPress | thingelstad.