Communication Leonardo (only ICSP Pins) and MKR1000

I have the following problem:
I want to communicate between a Leonardo board, which doesn't have free Pins any more, accept the ICSP Pins and a MKR1000.
I have already tried to use the SPI protocol, but unfortunately the MKR1000 doesn't have ICSP Pins and for this reason it doesn't work.
Furthermore, I tried to communicate over Software Serial Library, but the Library is not aviable for MKR1000 and so this failed, as well.

Does anybody know, how I can make this work? I have alreay searched the internet for some hours, but havn't found any solution.

Thank you very much.