Using setup-storage to encrypt swap partition

[Nat Sincheler]

My disk_config is this:

disk_config disk1 align-at:4k fstabkey:uuid
primary /                  2048- ext4 
rw,acl,async,noatime,errors=remount-ro
primary swap               4096  swap  sw
primary /var/cache/openafs 1024  ext2  rw,noatime
I would like the swap partition to be encrypted. How do I tell 
setup-storage to do this? Or do I have to do it using a script?

I am using FAI version 4.3.1 on Debian jessie.