No where in the PCF8833 data-sheet does it claim to use SPI, it uses a "3-line serial interface"
Software serial routines are absolutely trivial to write (and understand), adding a ninth bit (or more if needed) is simple as well - in this case you need to send that one first. Simply place the value you want on the data pin, and then apply a clock pulse to the clock pin, for the 8 data bits, do the same in a loop.
It's pretty well identical to what you do for writing PIC programming software, except it's more than nine bits