WORKAROUND
Problem:
Using Remote Desktop from MachineA to MachineB (B is the RDP host, A is the client)
On B (via RDP), you can normally browse or map a drive to \\tsclient\c in order to get to MachineA’s C: drive.
You can get to OTHER drives normally (e.g. \\tsclient\d is probably the CDROM drive)