Thanks to idbl_fanatic, over at Android Forums for finding this!
1. Install Anycut from the android market (it's free)
2. Open Anycut and select "New Shortcut"
3. Now click Activity
4. Scroll down the list of activities until you see "Select COM Port Mode" and click it. Just hit ok to accept the default name
5. You will see a "shortcut created" notification. Go back to your homescreen and look for the new shortcut
6. Once you click the new shortcut you'll see three radio buttons. Simply change to Mass Storage
1. Install Anycut from the android market (it's free)
2. Open Anycut and select "New Shortcut"
3. Now click Activity
4. Scroll down the list of activities until you see "Select COM Port Mode" and click it. Just hit ok to accept the default name
5. You will see a "shortcut created" notification. Go back to your homescreen and look for the new shortcut
6. Once you click the new shortcut you'll see three radio buttons. Simply change to Mass Storage