I know this isnt what you asked exactly … but I would guess it gets around your problems.
You could just make a swapfile that resides on your encrypted partition.
Below is a general instruction for creating a 8gb swapfile residing on root partition.
cd / && sudo dd if=/dev/zero of=/swapfile bs=1M count=8192 status=progress
sudo chmod 0600 /swapfile
sudo mkswap -U clear /swapfile
sudo swapon /swapfile
Now swap should be active. To make it permanent and activate next boot edit /etc/fstab to include
/swapfile none swap defaults 0 0
Thats it, reboot. You should have an active 8gb swapfile.