A wheel that is 8.0 - 8.5" wide with +45mm offset should set well within the LS' wheel wells. The wheels that can be questionable are normally around 38 - 40 mm offset. 42mm can be close, but you can ask some of the LVC'ers that are running them about where the wheel sits. Anything less than 38mm will may run the risk of sticking out a little bit.
Pektel has 19" 8.0 wheels with +42mm offset. Looking at pics of his car (he never wants to post them
), they look like they're close to the fender lips, but still appear to be behind them.
There are several LVC'ers that have wheels with a +38mm offset, and share that they do not rub. I don't know if that is in normal driving conditions or not.
What do you mean by "the flush look?" If you are wanting the surface of the wheel to be as close to the fender/body of the car, then you would actually be wanting a lower offset. The higher the offset, the more recessed into the wheel well it will be (again, depending on the total width of the wheel).