I can confirm that, at the time of this post, the Steam trainer works on the Epic version of the game when the .exe is manually added to it. 
However, because the game needs to connect to Epic Services first when it launches, you will need to wait until you are on the main menu of the game and for the “Authenticating With Epic” message to go away until you press Play in this trainer. Because it was designed with Steam in mind rather than Epic. Otherwise, the injection might time out and fail.
Enjoy.
I also agree with this.
For now there is a work-around, however. When overencumbered, turn on the “Instant Acceleration” cheat and increase the movement speed multiplier. This mitigates the slowdown effect of being overencumbered. You still won’t be able to jump, though, unfortunately. But it’ll at least help get back to base quickly to unload your inventory.