Reimu Marisa and Sakuya as the animaniacs.
Except the Animaniacs were
awesome. I would watch the shit out of that show.
Also, Yumemi for Brain and Chiyuri for Pinky would be more appropriate. Though I can see your point with Mima and Marisa:
"What are we going to do tonight, Mima-sama?"
"The same thing we try to do every night, Marisa-- try to take over Gensokyo!!"
... actually, any of the final boss+servant duos would work for that. Yumemi would fit the Brain role best, but Yuyuko and Youmu would be hilarious too... hm.