Wisconisn's 10 Electoral Votes can hardly substitute for Ohio's 20, but Tommy Thompson is probably the only Republican candidate who could carry Wisconsin. Even so, losing Ohio would make it tough.
As for the South -- sure, Fred Thompson could carry the South, but then again, so could every other GOP candidate except possibly Giuliani (who could still win most of the South -- maybe). Fred adds nothing to the Electoral calculus there, because our problem ain't in the South to begin with.
(this is not to deny that Fred may have some pull elsewhere, I'm just pointing out that he doesn't provide any unique advantage in the South)
Since he is from the area and well liked there, I think Tommy could also put Iowa (which went to Bush by a razor thin margin in 2004 and went to Gore in 2000) and Minnesota (which is often decided by less than 1%) in the GOP column. That totals 27 electoral votes -- with Wisconsin and Minnesota equaling Ohio's 10.
I do not think Frudy McRomneyson would play well in the great lakes and we'd lose those states to a ticket like Hillary/Richardson. Especially dangerous is the idiot freepers who seem to want to guarantee a Dem victory by saying "SCREW the rest of the country, we DON'T need 'em! Bush proves you can with ONLY the south and west!" Great strategy, assume the ticket can get every single southern and western state so we eek by the minimum 270 electoral votes. I hope these guys didn't use that strategy to pass college.