Looks like others are also working on this so I won't but this method should work as long as the new firmware is able to boot on the old kernel.The "kernel swap" root method has been working on recent updates for other sammy devices/variants and there is a strong chance it will work for you.
1. Install towelroot.
2. Odin flash the previous firmware's kernel.
3. Root using towelroot.
4. Flash back the new kernel. Done!
Someone that is rooted and hasn't updated needs to pull the ota update file from their cache/fota folder and make the new kernel available.