It has been quite a while since i dug out my LEGO collection, but i remember that the Mindstorms MicroScout brick could be programed via "VLL" or Visual Light Link, which if i recall correctly, amounted to aiming a LED light at the bricks light sensor and pulsing a series of on/off flashes to store a "program" to turn X#-of-revolutions clockwise/counter clockwise in a mixed series which could be selected instead of the built in modes.
This program stays in the device until the battery dies, or is replaced with a new program.
I think the "next step up" so to speak, of mindstorms programmable brick, the Scout (Not MicroScout) could also use VLL, but i never owned one.
There is actually a program to write a custom program and transfer it to the brick from the Sony Pocketstation console's LED (which was used as a form of communication between another Pocketstation).
Given that the 32k sidecar already has a LED, do you think it would be possible to write a program to flash the 32k LED in the needed sequences to reprogram the LEGO brick when aimed at this LED?