I haven't done this yet, but I am planning to after the birth of this baby. I had a moderate diastasis after the birth of my dd, and it took an excessively long time IMO to bring it back together (mostly). In the meantime, I felt that my core strength, back health, and general fitness were pretty seriously compromised.
I'm hoping to be better-prepared this time (and I do have a significant diastasis going on in this pregnancy). I think belly-wrapping or -binding makes a huge amount of sense, and it is standard practice among so many cultures that I have to think it is a good idea. I am planning to use a simple piece of cloth, and maybe a couple of diaper pins to fasten it.
I haven't been able to get much information from anyone on the internet or IRL who has done this, but I've read some about it in Aviva Romm's book about postpartum health, and especially in Robin Lim's book, After the Baby's Birth. My midwife totally supports my wish to do this, and will help me do it after the baby's born.
I've also read about some other practiced to urge the organs back into place, and the muscles to shorten, including certain types of massage and hot castor oil packs. I'd say the Robin Lim book has been the most helpful on this front. Have you looked at Elizabeth Noble's Essential Exercises for the Childbearing Year? I just got this book, and am *so* glad I found it. It's full of solid information about abdominal health before and after birth (and other topics, too). I feel that the author is totally and completely trustworthy when it comes to exercises to heal diastasis. (I've heard a lot of conflicting information over the years about what helps and what makes it worse.)
HTH a little!