By treating the ceiling as an allocated budget: identify which phases need this individual, count L time already used, and develop a second qualified employee well in advance.
Allocate the five years deliberately
Hypothetical example: The limit rewards planning and punishes drift. The first step is to count what has already been used, since prior time in L status reduces the available period. The second is to divide the programme into phases and ask honestly which require the specialist's proprietary knowledge on site and which can be handled by trained local staff or remote support once the capability exists.
The third is to develop a second employee who could satisfy the same requirements later, which is itself a timed exercise because both the qualifying year abroad and the acquisition of internal knowledge take real time and must be documented as they happen. Where the role would evolve into directing a function with staff, that is a separate classification to be assessed on its own facts rather than a continuation of the existing one.