Please let me know to specify drive letter to mount vhd.

I made WTG(windows to go) into vhd and copied external hard drive, and registered at BCD as one of pe.

The external hard drive is booted as Y: with Y-mount.exe, and at this time I want to mount vhd as W:. The vhd is mounting as L: now.

At the BCD file, I could not find the place to specify drive letter.
Click image for larger version
Is this possible?