Casper set hostname via dhcp in boot time ubuntu 12.04 live remix

[Johannes Amorosa | Celluloid VFX <johannesa@celluloid-vfx.com>]

I hope this is the right place to ask - If not I would greatly appreciate a hint where this should be posted.
Thank you for your time.

I'm booting successful via pxeboot a live ubuntu 12.04 remix. I want to set the host name via dhcp because I'm booting several instances of the same image.
Right now I'm using a hook line in /etc/dhcp/dhclient-enter-hooks.d/pinhostname that works quite well.

RUN="yes"
if [ "$RUN" = "yes" ]; then
var=`/sbin/ifconfig eth0 | /usr/bin/awk '/inet addr/ {print $2}' | /usr/bin/cut -f2 -d:`
var=`/usr/bin/dig -x $var +short`
var=`echo $var | /usr/bin/awk -F. '{print $1}'`
/bin/hostname $var
fi

But the dhcp server comes to late for munin etc and the hostname is not set in time. In the Casper log it shows me it receives the host name much earlier:

IP-Config: eth0 hardware address 08:00:27:86:3e:84 mtu 1500 DHCP RARP
IP-Config: eth0 complete (from 10.1.1.1):
address: 10.1.1.10        broadcast: 10.1.1.255       netmask: 255.255.255.0
gateway: 10.1.1.1         dns0     : 10.1.1.1         dns1   : 0.0.0.0
host   : storage1
domain : domain.com
rootserver: 10.1.1.1 rootpath:
filename  : pxelinux.0

How can I set that host name. I think I need to put a script in /scripts before I pack the initrd. There a loads of different scripts where would I put mine?