Instead of the search plugin you could embed Google Custom Search for site search functionality.
Unfortunately you need rawhtml enabled.
Once you've created your "custom search engine", just drop in the search box html like I've done in my Debian tips and tricks source.
If you have odd "save failed" error messages in Google's CSE's control panel, try /usr/lib/WebKit/GtkLauncher
from webkit.
Alternatively
You could use the Google plugin from version 2.67.