1 – Obviously you will first log into Google Reader and go to settings. Once there click on the ‘Send To’ tab
2 – You will see the default services listed and at the bottom of the page you will see ‘Create A Custom Link’
3 – Place your title i.e diigo in this case. Under URL put this ‘http://www.diigo.com/post?url=${url}?title=${title}‘
4 – For an icon I grabbed the 16×16 here http://www.iconarchive.com/show/web-2-icons-by-fasticon/Diigo-icon.html