Mark both waist bands at center, 1/4, 1/2, and 3/4. Pin them together at these marks. Using a ball point needle and a wide zig zag stitch. Stretch them at marks and sew together. Use more than one row of stitches,
You can get "insertion needles.". They have rounded points so they won't pierce but will spread the opening. Other end has a hollow area where jewelry fits in. Just push until one end of jewelry come out of piercing
I enjoy my nip piercings. Didn't really hurt more than an insect bite. I pierced them myself with supplies from Gauntlet Industries (needles, clamps, rings)