I tried to stretch them by just wearing them around the house, attempting yoga moves like warrior pose and a downward facing dog. Both attempts resulted in zero give. My last attempt: Google.
Google: "How to Stretch Jeans"
I had no idea that by spraying the areas I wanted to stretch (waist and thighs) with lukewarm water would let them give. Wow. All I did was fill the spray bottle with warm water. I covered the thighs with water and gave them a tug. Then I sprayed the waist and gave it a tug by stretching it out with my foot to hold it in place.
Result: The jeans buttoned with zero problem!
Who knew. Who knew. Thank you, Google and eHow. My jeans fit just in time for fall.