[Grml] Adding a program to grml-medium on USB-stick

Hello,

following your excellent instruction I installed grml-medium on a USB-stick thus eliminating the need to insert the grml CD whenever I want to do some minor data manipulations. For backing up partitions I use partimage, but unfortunately this program is not included in grml-medium. I have to "apt-get update" and "apt-get install partimage" each time I want to use it. Is there a way to permanently install this program (or any other) on the USB-stick? Hubert