To discard the data that has already been committed to the host, the FX2LP has to be switched to MANUAL mode. Implement the below piece of code to discard the data and re-enable the endpoint buffer to be filled by external master.
FIFORESET = 0x80; // activate NAK-ALL to avoid race conditions
EP6FIFOCFG = 0x00; //switching to manual mode
FIFORESET = 0x06; // Reset FIFO 6
EP6FIFOCFG = 0x0C; //switching to auto mode
FIFORESET = 0x00; //Release NAKALL