Can you swap out a CO or does the squad need to be reformed?
well....first, you have to sneak up behind him, and hit him in the head with your silver hammer. then you fire up your supercharged SAPP issue blender, and mix whatever happens to be around. add a little 100LL for that extra "punch".
now, simply steer him towards the tardis, and once he's inside, slip his podperson replacement right in. no one will be the wiser.