|Begin with a trouser or skirt pattern that has either no elastic, or elastic in the back half of the waistband. Construct as usual, EXCEPT when you get to the waistband!
You'll need two short pieces of buttonhole elastic, and a piece of regular elastic. (all the same width, ideally) Two flat buttons, and a little patience.
*Sew the two pieces of buttonhole elastic to either end of the plain elastic. (of course you can use all buttonhole elastic, but I don't have a lot of sources for it, and therefore choose to conserve.)
*Attach your waistband to your trousers/skirt, then put two buttonholes (for elastic to pass through) just an inch or two past the side seams. Towards the front of the item. The buttonholes should be towards the "top" of the waistband but not so near the edge that they disappear when the waistband is folded down and attached. Make sense?
*stitch the center back of your elastic to the center top of your waistband. (on what will be the inside.
*Put smallish safety pins on either end of your elastic, OR pin the length of it so it doesn't get caught in the stitching.
* carefully pin everything closed and finish the inside waistband. You should now have an ordinary looking waistband, but with buttonholes towards the front.
* Install your flat buttons.
* yank out that elastic and button it on thus creating your desired size!!!
***and then she noticed this had also been done on her favorite white maternity PENCIL skirt. It had a heavy t-shirt knit panel in the front, elastic in the front, along with buttonholes that were towards the back. Was a nice non-billowing silhoutte, and very comfortable.
***and then she also remembered that her son had a pair of bellow pocketed board short length bottoms that included pre-patched knees and fit him for well over a year. They lasted through three boys!!