Have them switch costumes

"Both of you switch costumes." You tell them. Both women without a word to each other begin taking off their boots. After that Power Girl takes off her cape as Wonder Woman begins removing her bracers and tiara. Then they both begin removing the main part of their costumes. You watch as Wonder Woman slides her costume down past her tits, two huge, perfectly shaped breasts. She then slides it down further, her perfect body now exposed. You walk around her to get a look at her well toned ass. Then you watch Power Girl. Her tits are even bigger and they jiggle as she wriggles out of her tight costume.

After they are both completely naked they hand their costumes over to the other. Power Girl starts sliding into Wonder Woman's costume, which proves to be far to small around the bust. Her nipples sit just above the gold part of the costume as Power Girl struggles to pull it up further. "It's fine like that" You convince her and she happily begins putting on the boots. Wonder Woman slips into Power Girl's suit, which is much tighter than her own. Being taller than Power Girl, the bottom half rides up her ass when she pulls it up to her shoulders, stretching the costume. The costume, though tight, is loose around the breast window, though it just manages to cover Wonder Woman's tits. "Pull your tits out of the hole." You tell her and she does before bending over to pick up the boots. They both zip up the boots then put on their respective accessories. Now fully dressed in each others clothes they give each other a confused look, not knowing why they switched.