No help but just a comment; In the days before improved IRSs with GPS; aircraft were "scattered" either side of oceanic airways, owing to poorer navigational accuracy - resulting in random lateral offsets. It is the improved accuracy and reliability of laser ring gyro IRSs coupled with GPS that makes track keeping so much more accurate and therefore SLOP sometimes desirable.
If you unofficially applied SLOP of just 1 or 2 nm over the Ocean, who is going to either notice or care? (as long as you remember to cancel the SLOP after the crossing).