Switchable balanced sum box/pedal question

[Jopn]

Hello,

A friend has asked me to build a pedal that has 2 inputs / 2 outputs (all balanced).

When engaged, he wants both inputs summed to one output.
When disengaged, the inputs will go to their individual outputs.

Can I get away with doing the following, and switching out points A and B?


Should I also put a 20k between the tip and sleeve of input 2 when bypassed?

Thanks!