Warning this will void the warranty I'm not much of a hardware tinker but I just had to open this up.
Since the passthrough was on my original test unit and the last one still had the holes in the case. I figured the main circuit board may not have changed much.
This one should be relatively easy to do as the circuit board still has the spot to solder in the hardware.
You can probably get the hardware from a old non working module.
You'll need a Drumel tool or something to cut the slots in the case to allow you to plug something in.
You can then just run two wires from the input to the out put legs, there are spots on the board to solder to.
I've not done this yet myself but I figure many will start moding this as the limitations are discovered and ways around them figured out. I don't know why the passthrough was removed. It couldn't have saved many pennies.
Since there are many in the community that like to tear things down this may be the perfect module to start hacking!