Ready your Tee and scissors.
cut just below the neckline, but don't cut the sleeves.
Fold the top part of the sleeves inside of the tee. Like origami! You're basically tucking the excess fabric in.
Sew just inside the seam that attaches the sleeve the sleeve to the bodice. I used my sewing machine but you could hand sew it.
Tack the bottoms of the sleeves up onto the side of the shirt.
Cut two slits on what used to be the top edge of the sleeve. (This part is folded under.)
Also do this in the middle of the waistband casing.
Cut two slits on the inside of the sleeve where the seam is. This seam blocks off the loop inside, so you need to do this to thread a string through.
Salvage four strips of fabric from the scraps. I took them from the back of the shirt under the neckband.
Sew two of them together end to end. Pull on all of them. They'll roll up.
(Sorry, no pics for this step!)
Thread the strips through the casings on the sleeves and the old waist of the shirt.
In the sleeves, you won't be able to thread through the entire sleeve. Use the slits you made in step 8 to continue the round.
(here's the pocket all sinched up)
Wear it upside-down and you're good to go!