Trigger "mount as disk drive" (aka "USB Mass Storage" mode) from PC
This app is designed to mount your phone as soon as it is plugged in. It seems to do your missing step.

Alternatively, this command (found from this forum) can be run on the phone (ex. adb shell) to turn on disk mode.

echo /dev/block/mmcblk0 &gt; /sys/devices/platform/usb_mass_storage/lun0/file 
Edit: This only appears to work in recovery.


Auto Mount App