Sadly in the Visual Studio 2010 release of IntelliTrace we didn't really have the time to give this custom event authoring scenario the respect that it really deserved. So while the functionality is still there we're not officially supporting this scenario in this release, meaning that you won't ever see official documentation on this scenario some place like on MSDN. I was actually planning to document this scenario more from my blog, but one of our more enterprising customers had already figured out much of this scenario and just finished up his own blog post on the topic of creating a custom IntelliTrace events. So I figured that I'd just piggy back on Guillaume Rouchon's excellent efforts and just link his article in here.
Customize IntelliTrace events (note FR language version also available)
Please do note the warning at the start of the article that this scenario is not officially supported in this Release. You can try pinging me on this blog for help but no guarantees with how much we'll be able to help. Also note that if you are making a large investment in this scenario that things might change as we try to clean up this scenario for a later VS release.