How do you mount the drive as a subfolder on C:?
Create a folder on your c drive called otherdrive or whatever you want.
Go into disk management.
Select the external drive, right click, and choose "Change drive letters and paths". Click the "change" button
Click the radio button "Mount in the following empty NTFS folder". Browse to the folder you created above ("otherdrive" in my example)
This is a handy trick if you are having rights/permissions issues with any drive that is physically on the same box. Files are written to the drive but treated as a folder in the C: drive.