If I understand it, you want to connect 2 devices to SPI and the board only has one chip select (CS) pin.
You can usually use another digital output as a chip select. When you need to send a message set the pin to the active state, send the SPI message and then set the pin to the inactive state.
You can also use another digital output to control a digital switch or multiplexer and route the CS to the desired shield.
http://www.onsemi.com/PowerSolutions/product.do?id=NL7SZ19
http://www.fairchildsemi.com/ds/NC/NC7SB3157.pdf
I hope that helps,
Steve Turner