How can I add a new search engine to Safari without any 3rd party add-ons?

I know add-ons such as Glims can do this, but I would rather stay away from them. Any native (or more likely semi-native) way to do so? If it matters, the engine I would like to add is duckduckgo.

The Safari Extension anysearch allows you to change the search engine used by the Safari search bar/unibar, without any hack-ish stuff such as changing the hosts file.

No, the only options are Google, Bing, and Yahoo.

If it is of any help, DuckDuckGo have their own extension on the Apple website for Safari extensions.

MacHints just did a post on this. The basic premise is that you redirect Yahoo! Search via the hosts file to the search engine of your choice. It works like a charm.