Installing Kali from ISO file in USB Drive failed

Hi. I use grub2 to mount the ISO file from USB Drive. It boots and works for live OS. But when I boot the installer, it stuck at the Detect CD-ROM stage. It should be easily passed by jumping to terminal and mount the usb drive, then mount the iso file to /cdrom. Unfortunately loop.ko is not available in installer so I cannot mount it by

Code:

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mount -t iso9660 -o loop /mnt/usb/kali.iso /cdrom

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. I have copied the loop.ko extracted from /live/initrd.img but insmod refuse to load it (dmesg shows something like signature mismatch). Besides DDing/writing the raw iso image to usb drive, anyway to do it?

Thanks.