If you wanted all parts of the hand to use the same 'material zone', you would need to edit the geometry. If your figure (or prop) uses an obj file for the geometry, then the easiest way would probably be to use the free utility "UV Mapper" to assign the same material (zone) to all groups in the hand. From the UV Mapper Edit menu use 'Select by Group' then 'Assign to Material'.

Another way to do it is through Posers Grouping Tool. The Grouping Tool will work even if the figure (or prop) uses geomCustom (internal geometry).

 

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P.S. I wrote the above before I saw markschum's post. Whilst I have never tried that method, I guess it is a equally valid way to go.