I haven't done it - but do you have a large size to compare the medium to? Then you could keep the wing span at the medium width, but trace the large for the rest of the body? Off the top of my head, I think you'd want the wing section to be longer (up and down, not side to side) as well as the crotch, or it might not fit around the legs so snuggly?
You might try cross-posting in the diaper making section if you don't get someone knowledgable here soon.
You might try cross-posting in the diaper making section if you don't get someone knowledgable here soon.