I always thought the best way to resolve this one was to promote someone for a post on acting-rank and then give them 2 shows on the Promotion Selection Board (PSB). If they score then they should be promoted to substantive, if after 2x PSBs they should be given notice or busted down a rank? If you want promoting to OF-3, OF-4 and OF-5 then you need to do IOD and ACSC(R).
That would then at least offer some parity and stop some of the sniping from the Regular cadre (which in some cases is probably deserved!).