Try this discreet stretch at your desk.

1. Sit up tall in your chair. Cross one ankle over the other knee to make a "4." Lean forward, bending at the crease in your hip where your leg meets your torso.
2. Fold over toward your legs in one piece, keeping a straight spine.
3. As you bend, lead with the chest and aim it toward your thighs, keeping the chin up.
4. Go as far as you can without curving your spine. When you feel your back begin to round, stop.
5. Take either your hand or elbow and press down gently on the knee that is crossed over the grounded leg. Lightly hold it there as you lengthen your spine a little more, trying to straighten it all the way down from your tailbone up through your shoulders and into the back of your neck. 
6. Lift the chin a little bit more.
7. For a deeper stretch, slightly increase the pressure on the knee, or just sit and breathe into the muscle.
8. Switch sides.

See a video on how to perform the stretch at your desk here.

Source: Lastics