Joseph and the Amazing Technicolor Dreamcoat (2000)
This movie is bonkers, and would make a sensational addition to the Rifftrax canon. It's only 80 minutes or so, but there's SO MUCH to comment on - insane musical numbers, intense eye contact, Donny Osmond - it's a plethora of Riffable Riches!
Additionally, you could invite NPH back or another well known thespian to join you for it. They would eat it up.