Principals should teach condensed summer school classes with full responsibility of attendance, electronic gradebooks, and SOL preparation. This would require the least amount of time committed to the task and give more of a sense of belonging to the school and the teaching community.
Most dedicated administrators I've encountered miss the classroom. There are a few who spend hours in the classroom, especially during summer months when the workload and discipline issues are at a minimum due to low enrollment numbers compared to the typical school year.
This would also require the administrator to maintain a current teaching license and attend mandatory professional development to remain current with best practice.