How to create an ETW session that is both real-time and saved to ETL?

[brycehutchings]

I am writing an ETW viewer (with a focus on real-time viewing), and I am using the Microsoft.Diagnostics.Tracing.TraceEvent .NET library because it looks like it has the most thorough support for parsing trace events. However, the one thing that I can't seem to do is create a real-time session that also logs to an ETL file. I have gotten multiple feature requests for this because my users want to watch their tracing in real-time but also have the ETL available to share if they encounter a bug.

The ability to do this is documented on the EVENT_TRACE_PROPERTIES struct:

If you specify only real-time logging and also provide an offset with a valid log file name, ETW will use the log file name to create a sequential log file and log events to the log file in addition to sending the events to real-time consumers. ETW also creates the sequential log file if LogFileMode is 0 and you provide an offset with a valid log file name.

As far as I can tell, this is not supported by Microsoft.Diagnostics.Tracing.TraceEvent. Is this something that could be added? It's a simple change to support through the Win32 API, but I don't know how much of this library has assumptions that they are mutually exclusive.