Hey there! I know this thread is a bit old but I decided to create an account here to help anyone out there might be reading this and who is or went through the same thing i did.
So my J-Pouch completion was in June of 2013 and I met my first boyfriend on July that year. I always thought I would be a bottom so getting the surgery devastated me. So for the first year I always topped and at first even certain positions make your scars hurt. Along the way he started by inserting one finger, then two, and 1 year after my surgery I was able to bottom for the first time. Keep in mind tho, It was very slow and a few strokes. So for the next year, I bottomed in total 5 times, no more than 10 minutes, and nothing hard or even deeper than 4 inches. This is because I felt my scars hurting around the sphincter and slowly they started to disappear. (the funny part was that everytime after we tried it I felt a lot better going to the loo, and much easier too)
After the second year, my scars had almost fully healed and he could go a bit faster now, but still nothing rough or deeper, and it felt much better now that the scar wasn't in the way of feeling pleasure. I even felt him hit my g-spot for the first time in forever. In the period of six months we did it 4 times and it was much easier than the first two years.
After 2.5 years, I don't feel the scar there anymore unless it gets irritated by what I eat, or if I go too much or eat too much. So I need to say that his dick is about 6 inches long and 5.3 inches thick in circumference, a bit thicker than average, and not too long. He now can insert it all the way and it actually feels good to have him inside me, it's almost a miracle in my eyes that I can do this after much heartbreak and suffering throughout these years. He is now my fiance and we live together and I honestly don't bottom much, probably once or twice a month, but I love actually doing it and feeling somewhat normal.
So in conclusion, it is possible, completely, as long as you and your partner have patience and are willing to cooperate in this together. Just be aware that you should let your anus rest and treat it like it's made out of porcelain.