An update for the 3d printable holder clips: There are now different options to mount the rails either against a rear wall, against a ceiling or between two walls.

check the picture. File names are self-explanatory.

Now uses M4 countersunk screws for better compatibility. Needs M4x10mm ideally.

To mount against a ceiling, just replace the M4 screw with a wood screw for example.

These print fine on an Ultimaker 2.