You are one dedicated woman!
I've used the cable cast-on before- maybe I just did it really tight, but for me it created a *really* firm edge. That was good for what I was doing, but for baby sleeves it might be too tight. You could do backwards loop, I think. Cable cast-on does leave the working yarn at the end of the newly cast-on stitches, which is where you need it to continue around the front of the gown.
Mommy to two wonderful girls
"I don't have to conform to the vagaries of time and space, I'm a loony!" -Campbell Bain (David Tennant) 'Takin' Over the Asylum'
OTN: Cabled Sweater
, arm warmers, kids' clothes