Here's one way:
You'd want to invert the GPIOs (shown here as switches). That generates an index value of 0-3 that can feed any index-selectable switch, filter, etc. I might omit the -1 term and set up the default (0) value as a pass-through or mute, in case your switch can generate an all-high condition if held between positions.
Also, if you are short on GPIOs but have an aux ADC to spare, you could use varying resistance to each switch position and a resistor from switch common to ground to create four different voltages, then use tolerance analyzer blocks to generate the index values.