How to set up ESP8266 HSPI to spy on a SPI bus

hspi_slave_begin.cpp

void hspi_slave_begin() {
    pinMode(SCK, SPECIAL);                  // Both inputs in slave mode
    pinMode(MOSI, SPECIAL);
    SPI1C = 0;                              // SPI_CTRL_REG MSB first, single bit data mode.
    SPI1S = SPISE | SPISBE | SPISCD | 0x3E0;// SPI_SLAVE_REG, set slave mode, WR/RD BUF enable, CMD define, enable interrupts
    SPI1U = SPIUSSE;                        // SPI_USER_REG.  SPI_CK_I_EDGE
    SPI1CLK = 0;                            // SPI_CLOCK_REG
    SPI1U1 = 7 << SPILADDR;                 // SPI_USER1_REG, set address length to 8 bits
    SPI1U2 = 7 << SPILCOMMAND;              // SPI_USER2_REG, set command length to 8 bits
    SPI1S1 = (length * 8 - 1) << SPIS1LBUF; // SPI_SLAVE1_REG, SPI_SLV_BUF_BITLEN = 12 bytes
    SPI1S3 = 0xF1F200F3;                    // SPI_SLAVE3_REG,, Define command 0 to be write buffer, others something doesn't match
    SPI1P = 1 << 19;                        // SPI_PIN_REG, Clock idle high, seems to cause contension on the clock pin if set to idle low.
    ETS_SPI_INTR_ATTACH(_hspi_slave_isr_handler, 0);
    ETS_SPI_INTR_ENABLE();
}

Is it possible to set SPI_SLV_BUF_BITLEN more than 64 bytes?