I wonder, would it be possible to replicate this method from the RE2 DLCs on The Messenger?
I'd try it myself, but I haven't played it past the intro, sorry.
I had this same thought a little while ago, when we were originally talking about The Messenger. The problem is that the Steam version of The Messenger doesn't have the extra DLC file that the Epic Store version has. With the Epic Store version, you can see an actual, extra file that's clearly there to enable the DLC in the base of the installation folder; the Steam version doesn't have that file, so I have no idea where the DLC data even is.