Thank you David and Ryan for your responses, a great help. I am now using the following in the BeforeRenderResponse event:
//This forces page to load in IE8 compatibility
try {
if (context.getUserAgent().isIE(9, 9)) {
var exCon = facesContext.getExternalContext();
var response = exCon.getResponse();
response.setHeader("X-UA-Compatible", "IE=EmulateIE8");
}
} catch (e) {
}