Yes it's been done by several people before.
However every time I've tried to contact one of them to buy one of those memcard they were never available or had no answer at all...
All the needed information can be found there:
I simply routed a very simple PCB (FM18W08 FeRAM and one switch to select between two 32k banks, each being equivalent to 8 original memcards regarding capacity):
Now waiting for the bare PCBs to come in the mail.