Question about Arria 10 and ALTDDIO

Hi,

I am using an Arria 10 device and I would like to use the DDR registers in the IO cell. The "serialization factor" I need is 2 (I simply want to drive two bits into the DDR transmit pins and receive 2 bits from the DDR receive pins). The ALTDDIO_IN / OUT library elements in the IP catalog in Quartus are "greyed out" so I assume they cannot be used in Arria 10. The "Altera LVDS Serdes" element only allows serialization factors down to 2. What do I instantiate in my RTL to get access to the DDR IO elements directly?