Create DIY for this, I guessing you are going to need to use 2 shirts, cut the one you'll wear with the side slits. Then cut strips out of Tshirt, sew into the inside of the first shirt at the top then weave and sew to the bottom of shirt.
crochet detail on t-shirt restyle - great way to make a shirt just a little bit smaller around the waist, or where you need it. (I've pinned something like this already, but here she uses a crochet hook and has lots of close-up pics.
truebluemeandyou: DIY Doily Tee Shirt Restyle Tutorial by Cathe for SC Johnson Family Economics. Very easy DIY. *I posted a very similar tutorial from By Hand London here, and then posted a tank where the front is a large doily by Trash to Couture here.