Three things to do:
1) add the search engine select to the "full search" as well (at the moment is available only for the quick search,
2) implementing an auto-detection, it can be done using the "opensearchdescription" link tag, an example:
<link rel="search" type="application/opensearchdescription+xml" title="popular-archaeology.com" href="http://www.searchplugins.net/createos.aspx?number=81239"/>
this leads to an xml file containing all the informations required
3) add a POST method (at the moment Elk uses a redirectexit, this supports only GET, but certain search engines may require POST (this will require some javascript trickery, either changing the action attribute and the name of the input of the form, or pass through a proxy page that will auto-submit via javascript to the search engine).
Modern, Free, Powerful