How can I make Windows not mount a drive when it is plugged in?

You could get a spare cord and cut the green and white wires. Then the computer won't be able to see it, because there isn't any way for the data to get to the computer.

If you're good with a knife I would carefully cut a 1 inch (25 mm) slice along the length of the wire. Then cut a slice around the wire, about in the middle of your first slice. You need to be careful not to nick the red or black wire. Then just cut the green and white wires.

Then just tape each end of the wires separately, and you have yourself a power cord.

I would like to note that USB ports aren't supposed to allow much current to go through the plug, until the device has connected. Since we prevented the two devices from connecting this won't happen. Many USB ports actually don't do this, so you may be fine there.

Some chargers pull the data pins high through a resistor, to indicate to the device it can pull more power.

The proper solution is via diskpart's automount disable command

C:\Windows\system32>diskpart

Microsoft DiskPart version 6.3.9600

Copyright (C) 1999-2013 Microsoft Corporation.
On computer: WIN81

DISKPART> automount

Automatic mounting of new volumes enabled.

DISKPART> automount disable

Automatic mounting of new volumes disabled.

DISKPART> exit

This doesn't answer your specific question, but I would look at using a USB charger instead of connecting the iPod to your desktop. Something like the Belkin Mini Surge Protector should work.