That splitting torque unevenly alone wouldn't be enough, as it wouldn't account for the effects in the angular momentum. Asymmetric differentials are typically implemented with epicyclic gearing which effectively provides different gear ratios at each output.
A convenient way to set up an asymmetric torque distribution is simply configuring different gear ratios at the front and rear differentials. This provides asymmetric torque at front and rear axles, as well as accounts for the angular effects properly in the same way as an asymmetric center differential does.
For example, setting up front-rear differential gear ratios of 2 and 1 means an effective torque distribution of 66% and 33% respectively. The general formula is: setting up gear ratios A and B in front and rear differentials provides torque distribution of A / (A+B) and B / (A+B) respectively.