I have done it, but I stripped the coating on the centre section of the Piegas and polished them first. They look great, sort of like vintage style bars and they work very well.
I’ve just done this for my build. I will say it is very hard. Remove the bolt completely and try to prise the stem open slightly when it gets tight. But it will go on.
26mm Deda Piega into a 26mm Cinelli 1A quill stem. Possible, or am I wasting my time trying?