Another idea just rushed through my foggy mind -
I could stack 4 or 6 of the pictured discs on a rotating shaft and use a motorized traction conveyor to shuttle the pieces under or over the spinning wheels.
The issue would be how to accomodate the differing heights of the tubing - the switch from one dimension to the next would have to be quick and reliable which would add some complexity. These wheels are also a bit pricey.
Another issue would be that the leading edge of the tubing would have to be at least clipped in place to keep the disc from grabbing it - many of the pieces are mitered so the leading edges might present a problem. I could poisition a leading edge clip or ledge on the belt to rectify this but again, it's adding a bit of complexity. I would also be concerned about balancing issues and wheel life.