Flash NRG 2 Panstamp while UART lines are occupied

Hi,

I am currently using the NRG 2 Panstamp in a design where the Panstamp is talking to another MCU via the UART lines.

Now I have the problem, that I would like to use the Serial lines of the Panstamp in order to program it. To solve this, I currently only see the option of using a 2:1 multiplexer, but its a bit expensive as it will only be needed once in the product's lifetime.

What is your opinion?

Best,
Henry