I found a solution to my problem after a bit of debugging. Basically, it's a bunch of For loops running in sequence to return the drive letter. Here's the code:
$oWMISvc = ObjGet("winmgmts:\\" & @ComputerName & "\root\cimv2")
$colDiskDrives = $oWMISvc.ExecQuery("SELECT * FROM Win32_DiskDrive")
For $oDiskDrive In $colDiskDrives
$CurrentPhDisk = $oDiskDrive.DeviceId
If $CurrentPhDisk = $CmdLine[1] Then
ExitLoop
EndIf
Next
ConsoleWrite("Selected right disk, selecting parition..." & @CRLF)
$sQuery = "ASSOCIATORS OF {Win32_DiskDrive.DeviceID='" & $CurrentPhDisk & "'} WHERE AssocClass = Win32_DiskDriveToDiskPartition"
$colPartitions = $oWMISvc.ExecQuery($sQuery)
For $oPartition In $colPartitions
$CurrentPartit = $oPartition.DeviceId
$PCMD = StringRight($CurrentPartit, 1)
If $PCMD = $CmdLine[2] Then
ConsoleWrite("Selected partition: " & $CurrentPartit & @CRLF)
ExitLoop
EndIf
Next
ConsoleWrite("Selected parition, converting to letter..." & @CRLF)
$sQuery = "ASSOCIATORS OF {Win32_DiskPartition.DeviceID='" & $CurrentPartit & "'} WHERE AssocClass = Win32_LogicalDiskToPartition"
$colLogicalDisks = $oWMISvc.ExecQuery($sQuery)
For $oLogicalDisk In $colLogicalDisks
$EndingDLetter = $oLogicalDisk.DeviceId
Next
ConsoleWrite("Drive letter is: " & $EndingDLetter & @CRLF)
And the console output is:
Selected right disk, selecting parition...
Selected partition: Disk #0, Partition #0
Selected parition, converting to letter...
Drive letter is: F:
