Going to give this my first try for something I have found, appears to work most days for a good few months. Please let me know if I say too much.

r/t (1), C1 - C2a, C2b - C1.
r/t (2) C1 - C2a, C2b - C1.
Single Legs C1 - C2a/b/c and C1 - C2a/b/c

All in for £397, 6 segments

Or drop one of the single legs to price out at £350

Still a large amount of fat left over but I was able to trim about 60%, I think it may be possible to do better.

Segments can be spaced out to have large gaps between return trips, single legs could be used as a placement flight or to form a return with a reward ticket.

Not the best deal in comparison to some of the fares found on here but hope it can help someone