Nigh on impossible and somewhat dangerous..... If you don't have a copy of the Haynes manual for the Renault 4, obtain one and read the section on torsion bar replacement. It'll help you appreciate what's involved!
It is easiest to fit the torsion bar with the hub, damper and tie bar removed from the lower suspension arm. You might just about get away with a large adjustable spanner after doing that especially if the suspension carrier was loosely fitted to the chassis and allowed to rotate.
It's not a real beginners job but after all not that complicated. Keep your mind to what you're doing and always keep in mind that there are pretty forces on loaded torsion bars, you've to unload the tension before you can remove them and after replacement you've to load the torsion bar.