I may eventually have the same problem, wanted to make sure it was large enough but may take off a few pounds in the mid-section. I've been thinking long and hard and THINK this might work for do-it-yourselfers: try taking it in by making an extra pleat at the very edge of the INSIDE apron, no moving buckles required just a slightly smaller inner apron. Use strong thread and remember this will have to bear the stress of the waiste-band. Remember if you do this that a pleat will naturally take DOUBLE what you want because of the fold. You can also consider stitching it down flat all the way to the bottom.

Please let me know if this does NOT work as I'm probably going to have to try it soon !