From what I can remember, that one you might be stuck with.
Your only other option is to buy a RZ/A1LU where they added DDR support to the QSPI. But, you just have to do the work of making sure the timing of the DDR QSPI chip matches up with the RZ/A1LU. I was seeing an issue that I could not run the DDR QSPI part on the RSK at the full 66MHz clock because of the timing violations, and the next drop down was 33MHz (but then you are the same as the normal 66MHz SDR...so there was not point).