The trick here is to profile the office application you're actually hosting your addin in, so Word / Excel / Outlook. I'm assuming you've got the addin loading on start up already, so you shouldn't need to do any further configuration.
When you try and start profiling, ANTS Profiler may warn you that you haven't selected a .NET executable, but accept this warning and carry on anyway. As the application starts up, watch the status bar in ANTS Profiler - it should change from "Waiting for connection..." to "Profiling performance of...".
I've just done a really quick test here in Office 2007, and it all seems to work nicely.
Hope that helps,