We have a kind of clunky, but workable solution for imaging a new
unsupported HP DC7800 workstation. This is only practical if you yaou are
dealing with a small number of machines.

We removed the hard drive and placed it in an HP DC7700, created the
image. Until we have a solution for the DC7800, we do a manual image on
the drive in a DC7700 and move it back to the DC7800.

This solution got us through a high priority installation of 5 machines
while we researched a solution.

Hope this is helpful,