Ramps to raise the whole car
 

I got this ramp for my 911 as you need to do everything from underneath the car but it is useful for any car under 2 tonnes.

https://www.youtube.com/watch?v=qtjxYkWqrIg

You can skip to about 3:30 if you don't want to know how to adapt it to work with a 911. It should be fine for a BMW Z3 straight out of the box.

Google CJ Autos for spec and prices

Nicely done. Even with the engine as a counterweight, I'd like to see a prop under the front of the car.
There are a number of discussions about this type of ramp over on zroadster.org and they are extremely useful. The only difficulty seems to be the ease of movement to where you want to use them- needs a concrete or solid asphalt surface. My drive is gravel faced.

Just needs to be able to roll along something as the base of the ramps get pulled together. A couple of scaffold planks would do it if you snuggled them into the gravel a bit first.