If you mean compatibility view in IE8 :http://blogs.msdn.com/ie/archive/2008/08/27/introducing-comp... then I'll have to agree that it would be better to handle the problem the same way (a button which would send a different UA string).

Think about the people who have to deal with the UA string for legitimate reasons (analytics...) they will have to deal with a special case (if (UA == "Opera/9.80...")).

It's seems a bit like a ugly hack to me.