I haven't done this job myself, so I'd rather let someone discuss it who has direct experience. I think if you do a search here on "flex disks" you might find some good info.
I'm pretty sure you will have enough clearance to work under the car with just the front up on ramps for the front flex disk, and the back up on ramps for the rear flex disk. If your car is like my 300-series car, its going to have two of these flex disks. You might consider replacing them both at the same time so that you have them all in new condition.
You are a lot safer with just having one end of the car off the ground.