I'm getting ready to do mine in my slanted driveway. This is the first time I'll be doing this on this much of a slant. I plan on draining the fluid with the vehicle in the driveway, putting the cover back on and adding one quart. Then back it into the flat part of the street by the curb and top it off to the correct level. I have pushed tons of vehicles in and out of shops with no fluid in the diff, as long as speed is low, there is enough residual fluid in the bearings to not do damage while moving the vehicle that short of a distance. The other thing your could do is purchase some of those mobile drive-on ramps to level things out.