I got around this by handling it all in JS / Jquery.
On a jQuery document ready clause I look for a specific type of anchor on page load and if that is present I assume that a message has just been posted. I then using jQuery display a nice little alert message up top of the page.
For the purpose of the sample code below I’ve used a standard JS alert function call to display the msg so you could alter this and make your own msg displaying function.
$(document).ready(function() {
// check for comment posts
if(window.location.hash) {
var urlHash=window.location.hash;
if(urlHash.indexOf('#comment-') === 0) {
alert("Thank you for submitting your comment. It will be reviewed and set live as soon as possible.);
}
}
});