Specific exercises for the low back and pelvis seem to help with back and sacroiliac pain. In particular, contracting the abdominal muscles that wrap around the waist (transverse abdominals) with one of the back muscles (multifidus) creates a natural corset or brace. This can reduce sacroiliac joint pain and prevent further pain.
Studies have shown that these exercises have a "nutcracker" effect on the sacroiliac joint. The force of the muscles contracting actually squeezes the bones that form the sacroiliac joint together. This action tightens the joint and helps hold it steady.
A physical therapist trained in spinal stabilization exercises can design a program that is safe and works for you.