Finally there is an official way of setting a text file as your Desktop Background: Windows Sysinternals BgInfo.
This tool can show a lot of information about your system but may also show the contents of a Textfile: Press the button Custom... on the right and then New.... There you may select Contents of a file and include a path to the text file.
After you saved the BfInfo config file somewhere on your system, you can call BgInfo in the following way to update the background image:
bginfo c:\System\config\bginfo.bgi /timer:0
This may be useful to show log files that you want to keep an eye on or the shadowfile of your favorite TaskWarrior report.