If Ricky Gervais can do a US accent, he'd be great as Darl. Otherwise, Kevin Costner would be a good choice too, if you could put a few pounds on him and ugly him up a bit more. Costner has a great deal of experience in the lead role of idiotic and pretentious money-losers ("Waterworld", "The Postman", etc.), so he'd be right at home.
As for Yarro, I'm thinking the guy who played Cigarette Smoking Man on the X-Files.
Liza Minelli would be a truly excellent MOG (although Joan Crawford would've been even better, of course.)
Mickey Rooney would be a great Daniel Wallace, and if he's not available, Andy Rooney from 60 Minutes would do in a pinch.
Brad Dourif could play Stowell; he'd basically be reprising his Wormtongue role from LOTR.
To play Herb Jackson, you'd want to find some no-name character actor, somebody who's usually credited as "Corporate Toady #3".
Since Divine is unavailable, Merkey could be played by either Wayne Knight, or John Lovitz, and I think Kirstie Alley would make a fabulous Didio.
Come to think of it, it's too bad Irwin Allen's dead. As the king of big-budget, all-star 70's disaster movies, he'd have been the best possible choice to direct.