I'd like it to start with something shocking, outrageous - a complete reinvention of everything we love that would make the Ben & Dan fans angry and hissing at their computer screens.
But then, at the very last moment it would all turn alright and perfectly fitting. And everybody would cheer about how they allowed themselves to be fooled.
I love this idea.
Maybe introduce a "Poochie"-style character, and the player is forced to play as them. Ben and Dan are now rich and successful, and refuse to work with each other (that's why the last game was cancelled, right guys? ;)). They've hired this new character to perform in the game for them, and they're just minor characters now, essentially doing cameos so they can honour their contractual agreements.
Dan in this world is very erudite and snobbish (the success having gone to his head). Ben is flamboyantly gay (the success having given him the confidence to come out -- although he's now a total "bitch" to everyone, too).
The puzzles are deliberately crap, and this new "character" doesn't have any real lines. Or frames of animation.
This is all just off the top of my head, but I do love the idea of trying to convince everyone that you've fallen out... Only for it to be a hallucination brought on by The Balloon Headed Mexican. Which in turn, actually turns out to be a hallucination brought on by a bad take-away.
And then the game begins proper.
Edit: Hmm. It's probably really obvious from the outset that it's not real, though, which goes against your original idea, Igor. It'd be great if something could be created that genuinely would fool people (who haven't read this thread).
Maybe a crate-pushing puzzle to begin with? Or maybe it loads up to a Tetris/Puzzle Bobble style mini-game where Ben and Dan stand on the side of the screen and cheer you on with the same three cheers, over and over. (Like a bad spin-off title.)