I'm in a similar boat as bluejoey, I have an automatic Vibe and a short commute to campus. I can bike to campus in 20 minutes, but my lungs can't take the cold air....no insurance to check that out.
Anywho, I have a permanent duct tape upper grille block. But for these short wintery trips, I have a removable lower grille block...a piece of garden molding jammed under the license plate frame and secured with duct tape. Simple, effective, and a tribute to Red Green.
The lower+upper grille block for short trips seemed to help warmup and help me stave off the awful winter FE blues.
(The lower grille did come off for long trips, though, otherwise the accessory fan came on, negating some fuel savings.)