Good call. I think I figured out from an amalgamation of comments made by Loop over time that "flush" is about 82.5mm out from the wheel hub in the front, and 87.5mm out from the wheel hub in the rear. (I'm sure he'll correct me if I'm wrong. You out there, Loop?

)
If a 9.5"-wide wheel calls for, at minimum, a 245mm-wide tire, that means you'd want a wheel with a +40 offset. If it's higher, you can use spacers to make up the difference.
In the rear, that'd be a +45. But if you're going to go with stretched tires/pulled fenders/spiffy camber, you can probably squeeze out a bit smaller camber. Especially if you're not as slammed as Alex is and I used to be. :P