Ooh, I'm glad I found this post!
I bought several pairs of jeans in my size, and found that two pairs had a smaller waistband than the rest. (I have a big belly, but kinda slim hips and thighs.)
This is what I'm trying: I slit the waistband at the side of the jeans down to the little button-type thing at the pocket. I'm going to add a kinda pizza shaped piece of fabric with a bit of elastic at the top. I'm going to do it to both sides, so it evens out.
Hope this helps!