Sorry for the resized pics, the subtleties of the fine art of image hosting escape me. In other words, #$%& you Photobucket, and #$%& you even more, PhotoPost.
Draw two lines down the back of your shirt in chalk or some other washable mark-y thing.
Then, starting at the top, make a mark every two inches on the outer side of each line.
...And cut down the line.
Now you're gonna want some 3-inch sections of ribbon. Cut as many sections as you have marks on the shirt.
Fold the first ribbon in half, and stab it with a pin...
...And pin it to the shirt where the first dot is marked.
Do this on every dot.
TURN THE SHIRT INSIDE OUT and pin the edges together like this.
Sew along the edge, pull the pins out, and turn the shirt right-side out.
Lace it up, and put it on!
The area under the lacing is o wrinkly because the shirt was much too big to start with. I should have planned it so the seam allowances were bigger. Ah, well.
ETA: Don't pull the laces too tight
unless you've gone over the stitching two or three times. Those little buggers'll pop right out if you really pull on them, and you have to pull out that part of the seam and put them back in. See that part at the top in the last picture, where the material's being pulled so tight it overlaps itself? One of those loops just made a jailbreak on me.