How on earth can a First Officer take command from a Captain who doesn't wish to relinquish same?
As someone mentioned, there are many ways to do this, like adding thrust. I remember once announcing to the tower that we were going around due to operational reasons. It worked for me.
And it was never an issue at the airline with a written two callout policy, because all crew know that they will not be supported if they ignore the concerns of the other pilot. Without such a policy, there is hesitation on both sides.