HttpHandlers / Modules :: Read Data Sent After A GET Request?

I'm in a situation where a GET request is made of my server without any content-length header. After the GET request is sent the client then sends a small chunk of data (8 bytes to be exact). It's imperative to note that this data is not meant to be treated as a request body. For this reason asp.net/iis ignores it. I cannot read it and the input stream says it has a length of 0. This is the correct behaviour!

What I need to do is somehow hook into the request processing pipeline early enough to read this data and somehow append it to the request (Items?) I don't know how to do this 'correctly'. I figure I should probably create an IHttpModule to check if the request is of the type that will have this data, then somehow read it.

How would I go about this? How would I be able to read this information in from the stream? I've tried adding an event handler to HttpApplication.BeginRequest but everything I try to read the stream fails. I've read that I could potentially add a custom header using reflection (this would allow me to add a content-length header) but this feels nasty and hacky - I presume there's just a place where I can hook in and handle the reading of the stream before passing it on for further processing.