SSR2013 (and SSSR2012) retention off-site copy

Dear,

I deployed SSR2012 for a customer. 1 recovery point per month, retention 6 months. Configured an offsite copy to a second disk.

All goes well. When the retention period on the BU disk is achived a clean happens as it should do. I notice that the cleaning is also done on the offsite copy disk. Is there a way that I can set a different policy for the offsite copy location? Actually what I woul like to achieve is 6 months retention on the BU disk and only purge content from the offsite disc when it gets full. In this way the BU disk would provide recovery for 6 months, the offsite copy would be long term recovery.

Thanks