Hello,
I am not entirely sure if I understand the steps you take correctly from your explanation.
But in case you inject the Peripheral RAM ECC correctable error, and it is reflected in MEMU, then all you need to do is to set up reporting to FCCU from MEMU.

Once setup, you will see NCFS0[18] flag set in FCCU when you perform FCCU read procedure. (not visible if you do not change OP to 0xA in FCCU CFG)
For fault reads refer to:
https://www.nxp.com/docs/en/application-note/AN5284.pdf
Best regards,
Peter