I unpicked the hem, and let it down by 2 cm. That was all I could do since the hem allowance was very small. Then I sewed on some ecru cotton lace trim by hand. The lace trim is from Daiso, 1.5m for S$2. Now the shorts is 3 cm longer.
There was just enough lace trim left for me to hand sew them to the back pockets as well. This re-fashion took 2 nights. One night to unpick the hem and another night to sew the trim. I love cheap and quick fixes for clothes.