^ I know what you're talking about!! They were in bright outfits... Maybe on a TV music show. I've definitely seen it, and now I need to know it too!
Update: extensive Googling in both English and Japanese turned up nothing... I'll need to dive into the video archives.
Update 2: YouTube prevails! I FOUND IT. High School Lullaby cover:
Isn't that what inspired Wagamama Ki no mama Ai no Joke's choreography?