The linoleum slip plates actually work really well. I bought the smoothest texture I could find (fake parquet wood tiles) and set them with the peel off plastic together so it's slippery plastic on plastic. I've tried rocking the car back and forth on the scale pads, jacked the car up or bounced the corners but using the cheap slip plates I actually see very little change after doing that. I set my notebook on the trunk and I see more change in weights. It's totally doable. Like I said though, setting up the pads before you set the car on them can be a pain. Setting a laser level on a pad that's sitting on a 1* angle will throw off the leveling process a lot so I'll set it on the center of the pad and shim the level until it reads zero. I have tape marks on my floor though to keep the pads in the same place and once I have it set I'm good to go.
I've shopped around and found better deals on leveling pads in the $400-500 range but the bookmarks are on my work computer, it's Friday and I have no intention of firing that SOB up until Monday.

I've also seen it done with a platform made out of 2x12 lumber.