First, you need ifcaro's fix:
Then, you need the dlc:
*You must beat CO-OP in order to play this dlc. This DLC is free and does not require ReactPSN. If you are confused to as to where the dlc is located in standard co-op mode just search "This is... Portal 2: Peer Review DLC" on YouTube. That video will show you where it is.
Lastly, you need my fixed 1.01 patch:
Now that you have all of the files. Follow the guide below. I suggest that you delete your Portal 2 game data before you begin.
Replace your Portal 2 backup's files with ifcaro's fixed game files. (I suggest backing up the files you are about to replace first)
Install the DLC package file
Install my fixed 1.01 patch (I modified the param.sfo so people should not need a spoofer)
This setup is working for me playing the game off the internal hdd with a disc in the drive. After more testing it appears to work discless or with a disc on both external and internal. You don't need to use bdmirror for it to work on external either.
NOTE: I have no idea if this works on 3.41 or other custom firmwares. All I know is that it works on Rebug 3.55.2 (with the latest update installed, it is a clean installation, meaning I have never installed it on top of any other custom firmware, such as Kmeaw).
If anyone would like to post this guide elsewhere and reupload the files to different hosts, feel free too.