Leave the circuit on the non RCD side but replace its MCB with a RCBO.
That way it has a RCD of its own and is hence separated from the main RCD.

And if the consumer unit doesn't have any RCBOs available for it, you can
install a separate RCD in a 2 way enclosure to protect an individual
circuit. You certainly don't want exterior electrics on a shared RCD.

Christian.