I just looked at the docs (http://www.sandisk.com/download/FCSProdMan.pdf) and have some thoughts.
It has at least 5 seperate Vdd supply pins, so this will not be easy to disable.
1> Pin 64 is labled TEST, if you put it in test mode it might disable it.
2> Pin 36 is labled RESET, if you keep it high IE continuous reset it might disable it.
3> Pin 40 is labled OI, selects IDE or PCMCIA mode, if you take it out of ATA IDE mode it might disable it.
4> If you play with the the configuration options, you should be able to set it up as a secondary controller.