John identified the need to use a shorting relay. This will avoid a momentary open condition. It will create a momentary change in overall resistance as one resistor will be bridged while two contacts are shorted. Whether this is significant depends on the values and how this is used.
I like Stan's approach of borrowing the detent function of the switch for a ganged potentiometer. It is fairly common to gang combinations of switches and potentiometers to a common shaft.
I would use a wafer switch with two or more wafers. Disassemble the switch to remove one or more wafers while leaving to detent in place. This will leave a portion of the shaft exposed on the back of the switch. It may be flat at this point as it fits a slot in the wafer. Fabricate a small metal bracket for the pot and include it when you reassemble the switch. You will need to couple the two shafts. This will allow you to use any value you require and change to a different pot if needed. Depending on the feel you want in the detent you may need to try a few switches.
