Is there any legitimacy to the idea of wiring the second, third, and fourth chips in sequence on a board, and then wiring that board to the onboard chip (the old daughterboard upgrade)?
Legit yes. Crazy yes.

Apart from the EMC type issues there's mounting the daughter board plus wiring every single pin by hand from the original RAM chips to the daughter board. Something like 56 wires. Don't think so.

If you could figure out a neat way to attach a daughterboard directly to the RAM, you might be in with a chance. But that would be impossible to solder I believe.
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Christian
#40104192 120Gb (no longer in my E36 M3, won't fit the E46 M3)