I’m guessing it won’t stay on the roller if you move the roller out closer to the end of the cup?
You might need to make something to go around the top steel lip area to raise up that end instead of trying to lower the butt. Used to be for the old rotary system there were 3d printed ‘forms’, maybe something like that, or a bit of round wood with a hole cut to fit the lip.
edit: or actually, some kind of plug type situation may be better, fits inside the opening and then the part sticking out could just be a larger diameter than the cup. the laser head would have more clearance then so be safer for it
not sure there is way to do this without creating some kind of extra piece really. I suppose some kind of thick tape around the bare metal part might be sufficient.
Apologies for this response being very stream of consciousness. The thick tape material seems like the simplest solution