You could try HD-Media Installation. I've done this on Debian in the past, i dont know much about CrunchBang. What it does it it boots up into the installer and then looks for the ISO image on the harddisk(HD) and continues from there.
You'll have to find HD-Media image of the version you are trying to install, and edit GRUB so as to display the hd-media kernel.On pre-GRUB2 versions this would involve editing the /boot/grub/menu.lst file. It would be something like this:
#this is what you'll see on the GRUB prompt
title CrunchBang 10 - HDMedia installer
#this is the partition where the hd-media kernel image & initrd is stored
#this is the location of the kernel image & the initrd within the partition
I've not used GRUB2 much, click here
for a how-to on GRUB2.
You'll need to place the iso image in another partition in your harddisk, place it on the root folder of the harddisk.
Boot into the installer from GRUB and if all goes well it would search for the iso image and the installation would continue from there.
If you have trouble finding crunchbang's hd-media images, you could try Debian's hd-media images. Keep in mind that the hd-media image will have to have to same kernel version as the kernel used on the version of Crunchbang to be installed.