It would seem that the CAA are not as unreasonable as some might think regarding what can be included in direct costs of flights in an owner-pilot aircraft and therefore shared in accordance with the regulations.
I understand that the CAA's legal department have verbally confirmed that maintenance costs that can be clearly demonstrated to directly relate to the duration of the flight (eg costs of component overhaul lifed on time, not calendar) can be reasonably included. Which is the sensible view.
If it is relevant to anyone I certainly think it is worth making your own enquiries to confirm this, rather than assuming such costs cannot be included.