That does sound difficult. Maybe do it bare-metal on a simple, non-MMAP architecture* with basic routines coded in assembler. Both main interpreter and JIT'd code might reference those core functions. I know it's not directly solving the problem but I sneak around the impossible parts wherever possible.

* Come to think of it, one of those microcontrollers or Java processors might come in handy here as they supply basic libs or RTOS's with primitive I/O functionality.