Whilst fiddling with a spool-holder design I got fed up of having to feed the 8mm bar back in and out every time I wanted to change something, so I present to you a drop-in bar holder for the G2S family printers.
There's a cup for the fixing ring in either side's version, so you can just have the ring on one end to secure the bar laterally, and leave the other free to slide stuff on and off.
You'll need 4 M3 screws of 5-12mm length or so to affix a pair of mounts, and suitable washers that the screws won't pull through yet are over 8mm diameter; I used M4's, primarily as that's what I had lying around, but there's minimal stress on the assembly so it shouldn't really matter what you're using.
0.2mm layers, 0.4mm nozzle
Print as oriented, with support.