I tried a couple of ideas posted here but they tended to break under significant load. I decided to try a slightly different approach in which there is no bulky rotating parts.
One output of the diffs is sent to the wheels while the other is sent to the opposite diff via a pair of worm gears similar to the ones that are located in the rotating part of the "normal" torsen diff. As in the regular torsen, the right hand outputs of the diffs rotate with the speed that is difference between drive shaft speed and half axle speed. As a result, it allows smooth turns but locks the wheels together when one of them loses traction.
As you can see in the picture, the forces that act on the worm gear part as quite large (the structure that holds the worm gears in place bent) so I need to make it stronger for real usage. I'll probably also replace the fragile 8-tooth gears with 24s (for the worm gears) and 16s. The fact that the structure does not have to rotate allows me to built is as robust as I want/need.
Because the whole thing is too bulky to fit in a classic live axle design I plan to built a model of Mowag Duro which uses DeDion type suspension in which the differential is bolted to the chassis. Real Duros have also a torsen center diff. Handling the torque there would be quite a challenge. Wish me luck!