the issue for kubica, apart from any mental block, is going to be his thumb and fingers, it's one thing to be able to grip a wheel again, another to perform the digit gymnastics todays F1 cars require, a good example being button's attempts to reset his KERS system in a recent race.
renault may well be able to move all the regularly used buttons / rotary selectors to the left side but there will be times in the race when multiple menu selections require both hands to be used whilst still steering and working the gear change paddles, it's possible you put both clutches on the left and make the gear change a pull push arrangement but it all increases the chances of a mistake whilst driving at the limit, that was one of the reasons the F duct was banned, the drivers felt it was unsafe to have one hand not holding the wheel yet kubica may have to rely on his injured hand / arm to steer whilst his left changes gears and adjusts brake bias, fuel map, kers program etc or deploys KERS and / or DRS all whilst battling with other cars.
i hope i'm wrong but i personally doubt he'll ever regain the absolute speed he had before his accident for anymore than a short run of laps