it seems strange that the software will allow me to choose any output for the charge pump though.
A little late, but just wanted to clarify.

Yes, you can assign the charge pump signal to any output. But the charge pump signal is a PWM signal. Only Port 1 Pin 1 has circuitry to convert the PWM signal to an on/off state. If you assign the charge pump to a different output, you'll just get the PWM signal on that output, which will not switch a relay.