I recently received a Google Cardboard viewer from Dodocase. It was fun to put together and worked really well with my Samsung S3 (even though the phone is a bit “dated” these days). However, in some of the cardboard demos I was “seeing double” and I think this was due to the default setup of the viewer and my interpupillary distance (which is slightly different for everyone). There is no way to customize it on phone without having a QR code, but there was no QR code on the case.
I found that you can customize the cardboard viewer by generating you own QR code using the following link.
I originally used the measurements that matched my case, but I found I had a “play” with the values a little to get them to work, but after a few tries it worked great! I found that using a “Inter-lens distance (mm)” or 55mm a little less that the actually measurement of 60mm and a “Tray to lens-center distance (mm)” of 35mm (1/2 my phone height width) worked well.
Good luck and I hope it works for your!