After my Monoprice Maker Select arrived, I was a little disappointed to find out that the filament spool holder thing they sent along with the printer wasn't large enough to accomodate a full sized spool. Well, with a 3d printer at my disposal, the obvious answer is to make a new one. This is just a quick little thing I modeled up in Fusion 360 and is large enough to hold a full sized spool.
The threads may be a little tight at first, but if you can manage to get the bolt on there and just screw it on and off a few times, the threads should work themselves out and they'll slide smoothly and easily. I printed this in PLA with a .2 layer height and that seemed to work really well, although it's not as pretty as it could be. Included in the zip file are the stl's for the rod itself and the bolt to secure it to the machine.