Hi!

I e-mailed Taro about that cel because I have one 
from that sequence too and could not ID it for 
the life of me. Stephen so nicely answered back 
and gave me the following information (I'm 
paraphrasing):

It was only shown once and was a special program 
called Suiyoubi Tokuban (aka Wednesday Specials) 
where Usagi and the other character (Super 
Bikuriman -- not sure of spelling) introduce 
their upcoming anime for the next season. He 
wasn't sure of the year though but if anybody has 
a copy of that episode, I'd love to see it. 
Here's my cel below (funky background, isn't it?)

Wendy