2. Mini Crunch/Pelvic Tilt: Lie on your back with your knees bent. Cross your hands over the abdomen as in #1. The mini abdominal crunch with arms pulling inward is the same as in #1. But this time add a pelvic tilt concurrently. To do so, tilt your pelvis backward so your abdomen is drawn in and your back is flattened out (likely you recognize this from early pregnancy exercises). Exhale as you do the pelvic tilt. Then lower your head slowly, and finally release the pelvic tilt. Repeat 5-10 times. Progress to 20, then 30+ repetitions. Only progress to #3 if your separation is <2 cm and has been improving as you have done #1 and #2.
3. Pelvic Tilt/Heel Slide: Lie on your back with knees bent. Perform a pelvic tilt (flatten out your back) and maintain it. Slowly slide one foot forward (making the knee straighter) as far as you can while keeping the pelvis tilted backward, then slowly return the leg to the starting position (still keeping the pelvic tilt), and repeat with the alternate leg. Every time you extend one of your legs, exhale. Repeat 3-5 reps on each leg. Progress to 5-10 reps on each side. Increasingly do 5-10 additional reps until you can do a total of 30-40 reps on each leg with full range of motion (knee becoming fully straight) and, of course, a proper pelvic tilt throughout.
4. Pelvic Tilt/Double Heel Slide. This is the same as #3 but performed with both legs sliding forward together. It is significantly harder than #3, so only progress to this exercise if it can be done with a maintained pelvic tilt throughout. Hold the pelvic tilt and slide both feet forwards, but not so far as to lose the tilt. As you get stronger, your range of heel slide will progressively increase. Practice slowly and exhale as you extend the legs. Then slowly return both legs to the starting position. Repeat 5-10 reps. Progress to 10-20 reps, then 20-30 reps.
Reference: Kisner C, Colby LA. Therapeutic Exercise; Foundations and Techniques, 4th ed. Philadelphia: F.A. Davis Company. 2002. Page 695.