I found this link in the comments section of an article on the 10th anniversary:
http://brokebackmountaintribute.blogspot.com/"The births, lives, secrets, times and deaths of Ennis del Mar and Jack Twist. What happened before they met, while they were together and....after that cabinet door closed?"
"...Brokeback Mountain Novel 1943-2006 by Vernon "Jet" Gardner
200 images and deleted scenes, covering every event from Ennis' birth in 1943, the deaths of Earl & Rich, Jack's childhood, the wreck that killed Ennis' parents making him an orphan, Jacks 1962 summer on Brokeback, Ennis & Jack's 1963 summer in detail, Jack's grizzly murder - with Ennis accused of it, Jack's parents' untimely mysterious deaths, why Jack was cremated and what happened to his ashes, and how Ennis survived 'til his own death in 2006... "
It appears to be a very elaborate epic, complete with maps and illustrations, that also includes the short story, the script and deleted scenes, in addition to the author's imagination.
I haven't read it yet, but wanted to post it for those who might be interested.