DIY Gamer Conversion

There's one more option, which is pretty hardcore:

• Create some in-line assembler to bit-bash out the display output
  
• Set up PWM on a pin with a frequency of 1kHz (to enable the timer)
  
• Use poke32 to set the interrupt vector table to point to your inline assembler
  
• Enable interrupts for that timer.
  
  

As I say, pretty hardcore, and probably not recommended :)