It would be wonderful if the script simply prompted you to type in the drive letter. The Powershell script could still display what drives were available and then just prompt for input of the drive letter.
As a side note, I'm forgetting something on the "bootcd" configuration, the USB key keeps prompting to create the zen partition and it can't be bypassed to get to a shell prompt and run img commands. I commented out the partition size in the settings.txt file, I guess I've forgotten my zenfu over the years. Our bootcds don't require us to create zen partitions but just go to a manual prompt, any suggestions?