Yanjun,
You can do this, but you will need to add the mass storage gadget drivers to the kernel first:
CONFIG_USB_GADGETFS=m
CONFIG_USB_G_ACM_MS=m
CONFIG_USB_MASS_STORAGE=m
Once you add these drivers, you will also need to disable the current USB RNDIS network on the board. Then, you should be able to do:
modprobe g_mass_storage file=/path_to_storage_file
Best,
Neeraj