Tried to retrofit my old model 3 blendmount in the S and it works as long as you grind off the ledge that sticks out...but, it did limit the angle of the rearview mirror maybe in the outer 5% range. It worked perfect for me at my seat configuration, but wouldn't guarantee it for everyone.
It appears that the mirror mount is at almost a 45 degree angle, and the blendmount bracket is flat on the bottom, with a slight edge cut into it on the top. I think the entire situation could be rectified by simply milling out the hole at an angle. Am currently working on some other projects and don't have time to do it properly, but will in the next few weeks. Might even reach out to blendmount and see if I can get the cad files to modify this and just cut my own then send them back a copy of the file so they can use it to make an adapter.
But in short, you can grind off the flange in the pic below and it should work fine for you.
It appears that the mirror mount is at almost a 45 degree angle, and the blendmount bracket is flat on the bottom, with a slight edge cut into it on the top. I think the entire situation could be rectified by simply milling out the hole at an angle. Am currently working on some other projects and don't have time to do it properly, but will in the next few weeks. Might even reach out to blendmount and see if I can get the cad files to modify this and just cut my own then send them back a copy of the file so they can use it to make an adapter.
But in short, you can grind off the flange in the pic below and it should work fine for you.
