One method I've found to work well, especially with engineers:
Make it clear to the team that the new leader is stepping up temporarily to fill a significant business need. That the engineer is doing the team a favor by doing this and that the plan is for it to be temporary because that engineer is a great IC.
It then becomes very easy for the new leader to go back to being an IC. They can even be thanked for stepping up to help the company during a critical time. They can also easily do it again in the future.
If the person is a great lead and gains the team's respect, then simply make it permanent.
Make it clear to the team that the new leader is stepping up temporarily to fill a significant business need. That the engineer is doing the team a favor by doing this and that the plan is for it to be temporary because that engineer is a great IC.
It then becomes very easy for the new leader to go back to being an IC. They can even be thanked for stepping up to help the company during a critical time. They can also easily do it again in the future.
If the person is a great lead and gains the team's respect, then simply make it permanent.