How to preseed encryption cipher?

I'm trying to preseed Ubuntu 12.04 alternate with LVM on an encrypted partition. But I won't use the default cipher AES.

With following code partman will use cryptsetup always with AES:

 d-i partman-auto/method string crypto
 # -or-
 partman-crypto partman-crypto/cipher select serpent
 partman-crypto partman-crypto/cipher seen false
 # -or-
 partman-crypto partman-crypto/text/cryptdev_description CIPHER serpent
 partman-crypto partman-crypto/text/cryptdev_description seen false
 # -or-
 d-i partman-crypto/cipher select serpent
 d-i partman-crypto/cipher seen false
 # -or-
 d-i partman-crypto/text/cryptdev_description CIPHER serpent
 d-i partman-crypto/text/cryptdev_description seen false

How it's possible to preseed encryption cipher? Any comments are welcome...