There are many custom spool roller designs. Here's mine. Press fits into the default spool roller frame on top of Printrbot Simple XL. Adds a wider track (for ~90mm spools) and a narrower track (for ~58mm spools). Printed mine with 0.3 mm layer height, 3 perimeters, 3 top/bottom layers, 0.1 honeycomb infill. Print two, obviously. I used "608" skateboard bearings. They're cheap - you can find packages of 8 or 10 for less than $5. I used some stray M3 bolts and small washers to hold them in place. I had to drill out the holes a bit.