Agilex5 transceiver in 64/66b mode

Hi, I'm working on a design to implement a high speed bidirectional interface using POC. To achieve highest throughput we should use 64/66 scrambling (which Agilex5 XCVR supports). It doesn't seem clear to me how to config the data bus and what option to select to run the XCVR in that mode.

when I select PCS66, I need to provide scrambled data (i.e. build my 64/66 scambler myself).
Selecting IEEE_MII port mapping is an Ethernet interface - which I don't want. So that's no option.
Selecting FLEXE_66 - well, again 66-bit bus meaning I need to scramble the data myself.

Can somebody explain how to get the internal scrambler to operate and how to map 64bit data from logic to the Tx_Parallel(79:0) bus?
What am I missing?