wireless - Add driver to my server installation media?

I am trying to install Ubuntu 14.04 server on a machine via USB. The machine only has a wireless connection and needs the wl driver (proprietary Broadcom STA wireless driver). Without this driver, the network detection process of the installation fails.

On this machine, I can install Ubuntu desktop via USB by booting the USB, running the following commands, then running the installation program.

sudo mkdir /cdrom
sudo mount /dev/sdX1 /cdrom

sudo dpkg -i /cdrom/pool/main/d/dkms/dkms*
sudo dpkg -i /cdrom/pool/restricted/b/bcmwl/bcmwl-kernel-source*

However, there are two problems when I try to install from the Ubuntu 14.04 server USB:

1. The dkms and bcmwl-kernel-source packages are not included with the server ISO. This is not a big problem since I can add these to my USB.


2. There is no dpkg program in the server installation shell.

How can I get my server installation media to have the additional kernel module wl?