Also, if you don't want this to be your default search engine you can still use Lucky search from the address bar.
Follow the steps as listed above except skip steps 7 & 8.
Remember what you made the Keyword field in step 4.
Now you can use that search by typing that keyword into the address bar and pressing the tab key.
This will allow you to use an I'm Feeling Lucky search, without needing it to be your Default Search Engine