Before you BO at the beg of the rows, mark out the center of the 48, which would be 24 and 24. Then BO 5, work 5 sts, dec 1 st. With a new strand of yarn, BO 26 (you have to knit 2 to get the first bound off stitch), dec 1 st and knit to the end of the row. BO 5, work 5, drop the yarn, pick up the old strand and work across 5 sts. BO 5 sts, no more left on that shoulder, pick up the the other strand of yarn, work across 5 sts, turn and BO 5. Then you're done.