Belle, my apologies for offending you.
You didn't specify the season in your post, and neither did the OP, but I did. The ship-home-the-dirties idea is not without pitfalls in summertime, which was what I was attempting to point out. I didn't assume that you would put clothing in boxes while damp, either, but I've lived in the deep South for most of my life, and I know what subtropical heat can do to boxed clothing. When you put clothing away in heat, it has to be free of perspiration residue if you don't want to risk damaging it. If you pack soiled clothing away in an air-conditioned environment in a warm climate, then put the boxes in a hot truck, they are likely to give off some moisture on their own, and plastic will seal that moisture in. There is bacteria in perspiration, even if it has had time to dry, and it thrives in warm, moist environments. Even after just a few days, the fabric is at risk of becoming permanently discolored.
If you wish to spend quite a lot of money on tipping porters and overnighting boxes, and time packing those boxes, that is your decision. I would suggest, however, that the amount of money you are spending on that process is likely to equal or exceed what the airline would charge for having an overweight bag. As the OP wanted to avoid paying an extra charge, packing light would seem to be the best plan in her case.