3 wire SPI 9 bit

i want to provide a module for a specific display driver, so far it works perfectly - when using 4 wire SPI

the driver provides the option to use 3 wire SPI, but the data must be 9 bit (where the first bit determines a command or a data byte)

so far i have no luck with

// add 'it is data' to the data by setting an additional 9. left bit
      data |= (1 << 8);
      this.spi.write(data, chipSelectPin);

is there some module where 9 bit SPI is used already?