Hi Alexander,
I get no script errors in IE 8 when I try using an overridedomain and sethash = false. I suspect it has something to do with either browser settings for script debugging or with hosting the ga.js file yourself. I believe the code is correct without quotes and would be incorrect with them.
Maybe I will look into adding the _addOrganic at some point but not now as I've already spent way more time on Google Analytics this week than planned and other things I need to do have not been accomplished.
Since _addOrganic could be called multiple times for multiple additional search engines, it does not seem like an easy thing to add. You can just as easily add javascript to the page/layout.master yourself to accomplish this, especially with the new async version, you can add a script block of your own that does
_gaq.push(['_add_Organic','somesearchengine.com', 'somekeyword', false]);
Best,
Joe