How about Stewie Attempting to Destroy The Muppet Babies?
Here's how I would do it (similar to the Mister Rogers parody):
(we see Stewie trying to kill Lois once again, and as usual, to no avail)
STEWIE: Oh, blast! This is even more difficult than when I tried to murder the Muppet Babies!
(cut to a shot of Baby Rowlf playing piano and singing "You're Special to Me")
ROWLF: (singing) People don't applaud when I walk by... I'm not athletic or good at jokes...
STEWIE: (interrupts him) In fact, I'm gonna die...
ROWLF: What the--?
(Stewie pops out of Rowlf's piano, with his laser gun)
STEWIE: Ah... yes. Those stupid little Muppet Babies Lois made me watch every morning. And now I'm here to seek revenge! In fact, why don't you look in that stupid neighborhood of yours?
ROWLF: Huh? (He peeks out, and we see the neighborhood on fire. The Muppet Babies run around, feeling scared. Fozzie even yells "Wocka wocka wocka!" in a panicky tone.) Oh, my gosh! Nanny! Nanny, look at the neighborhood!
NANNY: Oh, no! I guess I'd better call the fire department.
STEWIE: (to Nanny) And while you're at it, why don't you get me a doobie so that I can burn this stupid puppy after I smoke? Hey, hey, HEY! D**n you, vile woman!
ROWLF: I'm gettin' outta here! (screams in a panic)
STEWIE: Oh, well. There'll be other days.
(Knowing Seth MacFarlane, I'm sure he'd try and get Katie Leigh to do Baby Rowlf for this one. ;-))
Another one that comes to mind:
(camera zooms in on TV, showing logo of the E! True Hollywood Story)
ANNOUNCER: Now, back to the E! True Hollywood Story-- Muppet Babies!
(we see Baby Gonzo [and I'm sure Seth would want Russi Taylor to do him] in a play chair in the nursery)
GONZO: You see, by the fourth season, I was sick and tired of Animal always up to his antics every time he said "Gooooo bye-bye!" I was the unfortunate victim, okay? (He then smokes a cigarette, to which Nanny is in shock.) Piggy was always rude to me, and yet I still lusted after her. I wanted to be her boyfriend! (Baby Piggy walks up) Will you be my girlfriend, Piggy, my sweet?
MISS PIGGY:
I DON'T LIKE YOU, YOU WEIRDO! (screams really loud, then punches Gonzo in the nose with a loud "HONK!")
GONZO: (nose squashed) Snee nat I neen?
(Baby Animal shows up, next to a lever)
ANIMAL: Goooooo bye-bye! Ya-ba-ba-ba-ba-ba-ba-ba-ba-ba!
GONZO: W-W-W-hat are you d-d-d-d-doing, Animal?
(Animal pulls the lever, and Gonzo learns he's on an ejector seat. He's catapulted out the seat, screaming as he does, through the ceiling, and across town before crashing into the Griffin home. The Muppet Babies music can be heard as well.)