Add the bit to the control address (1110001x) to make a complete byte, where x = 0 or 1 depending on read or write. MSB first is standard so nothing to do.
Instead of DATAH and DATAL as bytes, use DATA VAR WORD.

sort of:
DATAIO VAR PORTA.0
CLOCK VAR PORTA.1
CMD_WRITE CON %11100010
CMD_READ CON %11100011
DATA VAR WORD

I2CWRITE DATAIO, CLOCK, CMD_WRITE, [DATA]