One of the most problematic questions for people being interviewed for senior leadership roles is about the broader experience. There are many ways to gain experience in more than one school leadership setting, some easier than others.
I recommend gaining experience by becoming a governor at another school. Being a governor is a meaningful part of school leadership. As a governor elsewhere they could performance manage the head teacher, make decisions about staff recruitment or redundancy, set budgets and make pay decisions. They would also gain valuable networking experience with colleagues and gain insight into how many of the more complex decisions are made in schools. Crucially they would gain an understanding of some of the legal limits of what a head teacher works within.