CP/M driver questions

I am attempting to build some code using BDS C for use on with our Model 100/102/200 memory upgrade ( http://bitchin100.com/remem_project.htm ). BDS C was the one (free) C compiler that I could find that had basic support for C syntax (it has pointers to structs, for example). Anyway, I have a few CP/M based laptops, an NEC 8500, 8401a, and an Amstrad NC200 (which can run "ZCN"). I'd like to use the NEC 8500 to compile some short C programs to 8080 assem and then use them on the Model 100. Here's the thing: the 8500 defaults to a mode where ROM takes 32K of the address space. It has several nice apps there but no programming language. I believe the machine has 64K of RAM, but the software won't let me switch to 64K all-ram mode unless I have an external drive attached (either a floppy disk drive controller or a ramdisk cartridge). I don't have either. In any event it's not real useful in all-ram mode without some kind of external storage containing applications and utilities. So here's my question: Can drivers for CP/M machines be loaded at run-time? My idea is that I could make a simple driver that communicates to some serial-based disk drive controller, or hopefully someone has already done something similar. How do I structure such a driver, and would it have to be part of CP/M or can I patch it in at run-time? -- John.