Just to conclude and pass on a hint. Eventually got around to testing this approach with a standard Ethernet card on an Arduino Mega and found the following works...
jumpers...
Mega pin 50 to card pin 12
Mega pin 51 to card pin 11
Mega pin 52 to card pin 13
setup() { ...
pinMode(11,INPUT);
pinMode(12,INPUT);
pinMode(13,INPUT);
SD.begin(4);
Ethernet.begin(...
I expect the same would work for the card I mentioned.