This is what we do as our major project during our VOICE unit - but it could also fit nicely into an Improv unit (it covers both requirements).
We teach the Elements of Voice, and give out the Telephone Conversations to build-up to this major project.
This project asks them, in groups of four, to create an improv presentation that sells an UNUSUAL product (funny prompts are included on the second page).
It also gives them a breakdown of the character types they have to use (example - a satisfied customer etc.)
They don't write a formal script, but rather use their improv skills to present, which makes for really strong presentations.
The kids get SUPER creative with this - it's so much fun.