Unfortunately, I am not aware of a way to fake a USB stick in any VMware product, but, this would be a brilliant feature.
Until then, one work around would be to create a SCSI virtual hard drive somewhere and mount this to your virtual machine.
VMware Workstation also has the ability to mount Virtual Hard disks to your host machine. If you uncheck the Read Only option, this should work well.
Obviously however, it will appear to the guest machine as a physical hard drive - for most operations, it will not make a difference, but, if you are trying to test booting, it may not be a reliable alternative as it will not match the real environment you are testing for.
The best thing you can probably do is to actually plug a USB stick in to your machine and connect it to the guest virtual machine. This should allow you to test the environment in the correct way as the USB stick will show as a USB stick to the virtual machine.