I fear there is no solution, at least not in LibreCAD. I tried it with Snap Middle and multiple middle points. It seemed to work, but the results were wrong, the parts were not of the same length. They looked like not being the same length by vision, and also Selected Total Length gave different values. These calculated values may also be wrong. Calculating things in ellipses is complicated in maths. Other CAD's I have tried don't give the length of elliptic arcs at all.