I want to make an argument in favor of getting in the way, with a twist. Getting in the way is an act of not following. It is more deliberately being contrary to following. This non-follower does not like the direction the leader is heading. The non-follower is trying to stop that direction. Oddly, this non-follower is also a leader. Such a person is making a case for a different direction, but often without doing the important step of proposing what that different direction should be. Therein lies the twist: If you are going to be a leader and get in the way, you need to take the extra step of proposing an alternate direction.
Be ready to explain your concerns with the initial proposal. Be prepared to explain why your alternative is better. Make your case respectfully, and if necessary, privately. Since you are expecting the other would-be leader to consider your case, you also need to be genuinely willing to consider a response.
Working together, you two would-be leaders should be able to figure out a good direction for the team. Consider how great it would be if every team had two effective leaders instead of one beleaguered leader and a non-follower.