You would think this would be a simple thing to do, but you would be wrong. I found an answer myself at Microsoft TechNet. Here's an adaptation of the code to do the job I requested:

use strict;
use Win32::OLE('in');
use constant wbemFlagReturnImmediately => 0x10;
use constant wbemFlagForwardOnly => 0x20;

my $flashdriveletter;
my $flashdrivename = 'foo';
my $computer = ".";
my $objWMIService = Win32::OLE->GetObject("winmgmts:\\\\$computer\\roo
+t\\CIMV2") or die "WMI connection failed.\n";
my $colItems = $objWMIService->ExecQuery("SELECT * FROM Win32_LogicalD
+isk","WQL",wbemFlagReturnImmediately | wbemFlagForwardOnly);

foreach my $objItem (in $colItems) {
    if ( $objItem->{VolumeName} eq /$flashdrivename/ ) {
        $flashdriveletter = $objItem->{Caption};
    }
}
[download]

The page lists about a zillion other attributes of the drive you can get from $objitem.

Steve