it will not help you ;-)
anyway ...
use a system with VMware Workstation.
Create new ESXi VM and assign a USB-drive or stick as a physical drive - do not attach it via USB !
This way the installer assumes you use a small harddrive and creates a small VMFS-volume.
I tried several variants of this approach - all the time a USB device was attached as a physical disk to either a new setup or to an existing one.