Tested in Cura, doesn't slice properly in Simplify 3D due to my lack of skill in creating models.
Work was done in Meshmixer and exported to STL. I took the existing female roller and cut the bottom off just past the provision for the bearing and duplicated it to make the other end and then put in a cylinder in between to make a one-piece roller with provisions for bearings. Confirmed that everything fits as expected.
Overall length of the one piece roller is twice the length of the female half of the original roller.
Roller_Merged_w_Bearings.stl | 3.6MB |