Without having tried the KnoppixLite but other small iso's.

The thing I've noticed is that the 'dialog' program has been removed which the knx-hdinstall uses.

You should be able to just copy the newest version of knx-hdinstall to your remastering iso (remember to copy the templates file as well), but you will properbly still be needing the command which couldn't be found.

Find out which command it is missing (look in the script) and from an original Knoppix do a:

ldd commandname

It will tell you which libraries the program needs - make sure they are on the Lite iso, otherwise just copy them, and then copy the missing command as well to the iso. Make sure the files are placed in the same folders as on the original Knoppix.