We used something similar to this. The child was facing backwards wedged in between the rear back and front seat. The two point belt went through slits to keep the seat frimly in place and the seat itself came with a five point type belt system to keep the child firmly in the chair. When they got a bit older I used a Römer Prince for Porsche chair.
http://www.dhd24.com/azl/index.php?anz_id=41330852