Snapmirror Cascade Reversal

I have a snapmirror cascade  A --> B --> C   

I need to run a test of this where the site containing A and B is down and I want to run on the C copy,  then when the site with A and B is fixed  reverse the sync.   

If I update, quiesce ,  then break the B --> C mirror then I can use the C to write data.    However then when I try operations reverse resync  i get  message the the volume is part of a cascade and to delete the other snapmirrors 

How can I reverse the copy so that A becomes the primary again without a full copy of the data again.