Write it out in mnemonics, translate ,by hand,from memory to opcodes (hex notation) and send it directly into unalterable masked read only memory. Should work first time right.
Anything else is for wannabe's.
ps: use lots of absolute jumps (GOTO) and globals with hardcoded addresses just to piss off the modular/reusable crowd.(because such programs run much faster since they don't have waste cpu cycles pushing and popping stuff onto/off the stack and moving data)