How about stitching two rows of binding tape down the centre of the front of the garment - with the crochet in between them. You'd need to do TWO rows of stitching (preferably on a sewing machine) - leaving a centre channel where you could cut up the centre. Then fold both pieces of tape to the INSIDE of the garment. You could perhaps trim the width of the tape of the inside piece of tape, so that it could be 'enclosed' once the outer piece of tape is folded under and stitched down again.
Can't think how you'd deal with the neckband though .
To go through chemo therapy or choose not to?