Hi, sorry to revive an old thread, but I had the exact same issue as you but I successfully added two fans to the GL12CP.
It is possible to remove the front panel and top to install fans.
Start by bending the side-clamps of the front panel outwards (Not too hard or they'll break like one of mine). Then you'll want to remove the front by pushing the bottom clips first, then the panel will pop out. (Note: a flat screwdriver helps pushing out the bottom clips. Also, watch the aurora LED cable when you pull it the front).
Once that's out, the rest is easy. Unscrew the 2 screws on top, and slide the top panel towards the front and voila, access to screwing fan location!