How do I use cycloneiii_crcblock if the CRCERROR pin is occupied?

We have a design, with PCBs already fabbed, that uses the CRCERROR pin (cyclone iii) as a general I/O. This can't be changed.

We would like to use the cycloneiii_crcblock, specifically so that the design running on the FPGA can extract its own CRC via the regout pin. Detecting CRC errors would also be nice but not necessary (yes, I understand that if the CRAM got corrupted you can't trust the routing from the cycloneiii_crcblock output anymore).

However I can't seem to convince Quartus to do this. If I activate the QSF option for CRC_ERROR_CHECKING then the build fails because the CRCERROR pin is used by a user I/O. If I do not activate that option then the cycloneiii_crcblock seems to do nothing -- the regout pin always emits zeroes.

Is there some trick for using cycloneiii_crcblock without using the CRCERROR pin?

Thanks.