Just open ~/Library -> Preferences -> com.apple.internetconfig.plist in TextEdit (or Property List Editor if you have the developer tools) and look for the WebSearchPagePrefs entry. In TextEdit, this is what my entry looks like:
<key>WebSearchPagePrefs</key>In Property List Editor, just add the "javascript" bit, which should be one long line, not five as shown here for narrower display (no spaces, no carriage returns, just one long line). Save the changes and quit the editor. Now start Chimera and Select Search Page from the Go menu. Cool, eh?
<dict>
<key>ic-data</key>
<string>javascript:q=document.getSelection();
for(i=0;i<frames.length;i++){q=frames[i].document.getSelection();
if(q)break;}if(!q)void(q=prompt('Enter Google Search Keywords:',''));
if(q)location.href='http://www.google.com/search?client=googlet&q='+
escape(q)</string>
</dict>

