Disassemble the fan to get down to just the motor and the blades. Retain the long self tapping screws that held the motor to the plastic frame.  Use them to attach the motor to the object as shown in the photos.

The SCAD could be modified to fit other fan types, it's fairly parametric.

The top bit is a bit more overhang than normally would print cleanly, but it doesn't bother me. If it does bother you, you might use support, or change the SCAD to reduce the overhang area a bit by increasing the height of the mount plates (this will increase the amount of plastic used when printing).