I'd like to be able to define in my LVM configuration file :

d-i partman-auto/disk string /dev/<%= @host.params["dev_disk"] >
d-i partman-auto/method string lvm
d-i partman-auto-lvm/new_vg_name string vg-<= @host.name >
d-i partman-lvm/vgcreate string vg-<= @host.name >
d-i partman-lvm/device_remove_lvm boolean true
d-i partman-lvm/confirm boolean true
d-i partman-auto/expert_recipe string \
my-recipe :: \
100 100 100 ext3 \
$primary{ } $bootable{ } \
label{ boot } \
use_filesystem{ } filesystem{ ext4 } \
method{ format } format{ } \
mountpoint{ /boot } \
. \
20480 20480 1000000000 lvm \
$primary{ } \
$default_ignore{ } \
method{ lvm } \
vg_name{ vg-<= @host.name %> } \
.

But the variable aren't interpreted. I understand why when looking at the preseed template, but I'm sur their is a way to make it work