workout targets your entire upper and lower back, core, hips, and glutes. Do it two or three times a week (three sets of each exercise, working up to 12 reps per set) to improve your posture, prevent aches and pains, and achieve a strong, defined rear view.
Or mount the mirror to the front of a shelf. This is a pre-made piece from Norm Architects and retailer Ex-t (spotted on Dezeen), but it's easily DIY'able. (It reminds me of decorators who mount framed artwork right to the front of their bookshelves.)