You can use UDB based SPI Master componenet. Connect 1:4 Demultiplexer on the slave select pin and thus generate 4 slave select signal. This design is given in the SPIM component datasheet, Page 4. Please refer to that.
Or you just handle the Slave Select signals manually in firmware, then you can use also the fixed-function SPI component.
Remember - SPI works mostly like a bus, except for the select signals. Or do you need to handle parallel transfers to multiple slaves?