Is your processor a master or slave? You can't select a slave device, but you can combine the shift in/ shift out functions to use the same clock line and data pin. I did this for some PIC to PIC comms. The clock line rode high, when the master wanted to communicate, it would hold the clock line low until the slave pulled the data line low momentarily. Communications then commenced. The master was using PBP with shiftout, and the slave was using assembly for an on screen display. It worked great.