response group concurrent calls

Hi,
we have a response Group of 12 agent configured in round robin and we really enjoy how it is working but
now we have a new requirement, and then we should handle only 2 concurrent calls at a time,  there is a way to configure this in Lync? (please remember that the response Group has to be  composed still by 12 active agents so that calls can be passed between people)

Thanks,

A.C.