Thx @bestlux
After further work with a magnifying glass I determined that I needed to unlink row A of the jumpers (hard to cut tracks). And link row B. So now we have SD on 4; MOSI 11; MISO 12; SCK 13. I thought it should be possible to use the standard Arduino SD library with #define SOFTWARE_SPI to create an SPI master on those pins. That did not work.
Then I tried SD.begin with 4 params, specifying all SPI pins. This is working OK. Next step is to ensure this can co-exist with an SPI slave on the same Leonardo.