You could do it several ways, but below is the closest option to how you propose in a binary sense. Use 2 virtual auxes - you only need 2 as the 3rd combination would be assumed anytime the other 2 are not true.
The other other would be to receive the data as a two bit value - say use something like CAN AN Volt channel, then the 3 switch positions could be represented as a value 1/2/3. You could put the CAN AN Volt directly onto the boost table axis.
