Good news.
I found a solution that will allow you to get Lumen without seams, and I also checked this solution for stereo, it seems to work.
I am currently developing an automated solution, it is difficult to name the deadlines yet.
In the photo you can see that there are no seams in the upper part of the projection.
I have to do a lot more work before I can make this possible.
You, in turn, can use 6 task rendering twice, for example. First, render your camera at the -3.2 mpx position, this will be the left eye. Then change the position to +3.2 mpx, it will be the right eye. The total distance between the eyes will be 6.4.
Then you can combine the images in any program.