To keep the copes oriented the same way I'd tack a chunk of 1.875" on the back one and let gravity keep things lined up, or have a helper hold it with a level while I secured it, if it was being particularly difficult.
Do you have a center head? Mark center of pipe at each end, take a straight edge, or chalk line and make a mark from one end of the pipe to the other end. Transfer this mark to the opposite side of the pipe. You can even quarter the pipe if you want to.
I have a job coming up where I need to cut 45° miters on each end of a 2' piece of tube, and I'm scratching my head how I'm gonna keep the miters aligned. The ends of the tube will be fit into a corner, so they need to align along a right angle. The tables on the bandsaw and mill aren't much help because they're either too small or oriented wrong to let me use a miter gauge. Your idea of tacking a length of something to the first miter just might work, but I'm open to suggestions... :confused3: