Watching a trailer on YouTube "From Bedrooms To Billions" http://www.youtube.com/results?search_query=bedrooms+to+billions&sm=1

One of the early developers (programmer in those days) talks about hooking a Vero board to one of the (only) ports a the rear of the ZX Spectrum; or it may have been hooked up to the main board... This was to enable ease of entry of code (Z80 Asm) whilst also circumventing use of the (nasty) keyboard. I believe he may have used a cross-assembler and downloaded the code across the Vero. I think he was a engineer of sorts so this would be well within his scope.

Now for a noob question(s)...
How would this have been achieved ?
Does anyone of someone who has done something similar ?

<bump> I have since found what this could be. In the early 80s prior to the existence of any development tools, early assembly coders would avoid coding directly on the machine. In the case of the Spectrum, with the unsavoury keyboard and lack of a decent m/c monitor, a board was plugged into the parallel port. This board was known as a "Softie" and contained a EEPROM emulator. Hex code was input directly to this and mapped to the memory of the machine.
Although this is of historical curiousity it is interesting to see how some the iconic games of that period were developed. Can anyone verify this ?

He was probably just programming the microcontroller just like we do today with AVRs, PICs, and <insert many more microcontroller names>. What he had built was probably a homebrew programmer.