i did! i went to david's bridal and they were pretty accommodating. they had these fake bumps to try on and i ended up getting an empire waisted dress that was 5 dress sizes larger than what i normally wear and they adjusted it as the day got closer. but then i didn't get married. go figure.
I didn't need a maternity dress, but still got my dress custom-made for me by a friend, who's a designer. I think this would be the best way to go. She kept adjusting the size of my dress within the 5 weeks from first measuring to wedding day several times because I dropped so much weight, and did the last adjustment the night before the wedding. I think if you really want a dress that fits perfect, going for a custom-made one is probably the best option.