C84/Oneshot - Impedance selection/mod

[BluegrassDan]

Just built a C84/Oneshot. Since the "IN Z" switch is inactive due to the transformerless design, is there a way to add input impedance selection between either 1.5k (default) and 15k (or some other higher value)? I built this to go with my RCA 44bx which might benefit from the option of a higher impedance.

Any thoughts on how to make this switch usable in this manner?