Many examples are listed in the Poorly Disguised Pilot entry at TV Tropes.

Before I read the whole post, I was worried that you were going to mention Top of the Heap.

Thanks for that link, DevilsAdvocate. It's always fun to spot these episodes when watching re-runs of a long defunct series, especially when hindsight tells us that the attempt at spin-off must have ended in complete and utter failure.

I was recently watching an episode of Diff'rent Strokes (shut up) and after 2-3 minutes of standard funny business with the regular cast, the focus switched to an entirely new setting—a night school classroom, where Arnold's teacher Miss Chung was starting a new job teaching an adult ESL class. Of course, all the sitcom tropes were in place: the multi-ethnic cast, the Latino street tough, the cute old married couple, the dim-witted but kind-hearted fatso, and the Balki-esque oddball from some vague region of Eastern Europe. It was as if some network executive had been given a "boffo" pitch by the hackiest writer in hacktown, and on that basis green-lighted a series he felt would be a sure-fire hit, but then never bothered to develop it past that rudimentary starting point.

The result? Miss Chung was right back trading quips with Arnold and the gang a few episodes later.

Balki-esque oddball hee yer funny Atom Eyes

the hackiest writer in hacktown

How does that gig pay?