For this purpose there is a stock conversion kit from Weber to buy. We decided against the original because we the hose was too short and the price is too high.
Instead, we ordered this set. The pressure reducer has also 50mbar and you get a 20cm longer (total 80cm) tube than the original conversion kit from Weber.
The retooling my friend had then done also within minutes. Since then we grill successfully with a 5kg bottle gas.
I hope my review has facilitates the buying decision a little! :-)