Force IE7 Compatibility Mode in IE8

We are migrating to IE8 and we wanted a way to force this. It seems that you can add a meta tag in the header, but that would have taken days with the number of pages we would have to change. I wanted to know if there is a simple way in IIS to do this. It turns out that someone else blogged about the same thing here. It seems that meta tag can easily be added as a custom HTTP Header and we are all set.