I just wanted to share my experience.
First of all, I could not make VirtualBox to see USB devices. No matter how much I tried, it refused to show them. And believe me when I say I tried. I did all the suggestions out there. Including installing the extension pack and adding a filter with my device IDs. But it just did nothing.
So I turned to VMWare as an alternative. This time, at least I could see my USB device on the guest machine. But now I could not list the USB device as a installation destination. The installation dialog only shows virtual drive defined by VMWare and that’s it. I tried deleting USB’s partitions and even creating new ones but the USB was never an installation destination. I also tried adding this line to the .vmx file of the VMWare virtual machine:
firmware="efi"
[SOLUTION]
I’ve found what was wrong in my case. I needed to change the partitioning of my USB before it was accepted as the installation destination. I used KDE’s partition manager and I created a new partition table of type MSDOS. Then I created a new partition of FAT32 format. Then everything worked just fine.