I like the sound of your idea

do you mean that the pump and the larger machine are joined together to make one machine? That would be awesome.
Along those lines, I was thinking that the pumps could be first on the table, as 2 pumps would be needed. The player would firtst connect the pumps to the larger machine, as they would connecting the black dildo or the vibrator to the fuck machine that is already there, then they would command the girl to get onto the milking machine. The next step would be to connect the pumps to the girl. Them the player would control it as they would the fucking machine.