It can be done since CPU has all the required pins. I had thought about it and added something like a micro SCSI connector wired to the CPU and making a custom cable that connects micro SCSI connector to that 3x23 pin connector for CD drive. Never tried it at all since CD^2 aren't portable and they are too bulky to properly hack for portable play. Super CD-ROM is too valuable for me to even think of ruining one.
Converting Duo to portable is probably easier. Someone was able to cut a Duo in half and made it a stand alone non-CD system. Portable version can be done by cutting the board in half, folding the CD drive and CD board over to the back, and rewiring them all then bulding or 3D printing custom shell. Another drawback to portable CD is they aren't power efficient as later CD consoles like PSOne with Duo sucking up almost 1.5A plus more for LCD.
Cool hack if the picture is legit.