i think you could make this with tunisian. when it gets the the split, you could keep working half the stitches until both halves are long enough and then start stitching across the entire piece again at the other end.
El tejido es con dos agujas, pero las imágenes dan una buena idea para hacer un bolero con un rectángulo. Yeah, that's what I was gonna say. actually this can be done knitting, crochet, material as it is just a rectangle sewn to make sleeves!