Start restore from harddisk

Hi,

We have succesfully created a ZEN Boot Imaging partition and stored
the image file on the root of this partition.

However, we are unable to find out how to automatically restore
this image file to a second partition.
This restore should be fired off at the moment that we boot
the PC with the Boot menu (option Imaging).

In the settings.txt file on the harddisk, we changed the IMGCMD
line, but no success yet.

Someone has done this before ?
Are we missing something obvious ?

Thanks for any helpfull tip.