Everything is possible as long as you have the money and the patience...The thing I learned by modifying my cars, is that it is always more difficult as it first seems to be...
The memory feature is connected to the seat and mirrors as well...I think that the W124 should be one of the easier models to add memory, but only after taking out half the interior and power seat wires.
I have considered this for my C class as well, but think that it will get too expensive (but it certainly IS possible).
greetingz from a MB-modifying -nut,
with a minor 600+k