Isn't the BNC model managed by default and thus includes the Subnet Manager? at least that's the way I read the manual here:
http://www.mellanox.com/pdf/user_manuals/InfiniScale_IV_36_port_Switch_UM.pdf
Page 22 says the subnet manager is included for internally managed systems, and page 6 shows the BNC code means Managed IB RoHS.
thanks