I think it is too late to "modprobe ehci-hcd" once the system is running, because usb-storage module will be loaded by then and
it will probably cause a kernel crash.
Therefore suggest to make a new CD.

To make the CD, you can follow the "Knoppix remastering guide" - it takes a while and requires a fair bit of disk space, but it is an educational experience!

Before building the final ISO image, use this procedure to edit the linuxrc file:

cd /mnt/drive/knoppix-tmp # assuming that is where you are building the release
cp ./master/boot/isolinux/minirt.gz .
gunzip minirt.gz
mkdir /rt
mount -o loop minirt /rt
vi /rt/linuxrc # i.e. change USB2="ehci-hcd.ko" to USB2="ehci-hcd"
umount /rt
gzip minirt
cp minirt.gz ./master/boot/isolinux/minirt.gz

Hope this helps,