Short answer:
No, you cannot directly use a McIntosh C12000ST preamp module with a McIntosh C500 controller. They are not electronically or mechanically compatible with each other, even though they look superficially similar and follow a similar "dual-chassis" concept.
Various reasons which include, different internal architectures, proprietary interconnects, firmware/software incompatibility etc etc. Unfortunately there's no safe or practical workaround.
A possible solution might be to try and source a demo controller from a dealer? I'd think that most people would buy the complete stack together, which would make sourcing the controller seperately quite challenging.