@Mark - I'm the last to give any wedding photography advice but one thing I do remember reading about through all the research I did when I was going to shoot my one and only was to not ever shoot the bride straight on. She should always be angled to the camera or it just makes any bride appear heavier than what she is. Or you could try the liquify tool in photoshop, thinning people is one of the main things it is for and by the time you are done applying it to 300 photos of the bride, you will be an expert at using it!