According to the manual, it's possible to make a cluster on a target object, select the cluster and then select a deformed duplicate object to create a shape key which is only applied to the components in the cluster, with any other deformations being ignored.
This would be pretty handy, but all I get is
"' ERROR : 2006-ANIM-SelectShapeKey - Unexpected failure. - "
does anyone have any ideas about how to do this ?