knoppix 7.6 usb boot persistance

hi

i curently have a knoppix 7.6 usb boot straight from iso file stick (using grub4dos) and im stuck on creating the knoppix-data.img file
-i tested a boot from dvd with boot: knoppix tohd=/dev/sda1 mkimage inside a virtualbox.. this line actually copies the dvd image of knoppix and after that it prompts me to for the size of knoppix-data.img; considering the knoppix-data is portable between systems i can copy the file on the usb stick and go from there

-how can i create the file without copying the knopix image on hdd(i tryied as a kernel param but didnt work kernel... mkimage; i also checked but didnt find an inside knoppix desktop command to create the data.img file but didnt find any)
-how can i link it to the booting process .. as a kernel param

ps: ive checked gogle.. but its quite a mystery although its a handy way to keep settings

ty

There is already a ton of threads on that subject in this forum. Just do some search.