don't know how thought policy edit, but this is how you done on stand alone workstation:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer
add this key:
NoDrives REG_DWORD
The low order (right most) bit is driveA: while the 26th bit is Drive Z:
To hide a drive, turn on its' bit. These drives will still appear in File Manager. To remove File Manager, delete winfile.exe.
If your not happy working in Hex, add these decimal number to hide the drive(s):
A: 1, B: 2, C: 4, D: 8, E: 16, F: 32, G: 64, H: 128, I: 256, J: 512, K: 1024, L: 2048, M: 4096, N: 8192, O: 16384, P: 32768, Q: 65536, R: 131072, S: 262144, T: 524288, U: 1048576, V: 2097152, W: 4194304, X: 8388608, Y: 16777216, Z: 33554432, ALL: 67108863