I'd say drop the plasma pistols from champions and squads, as they aren't really worth it. Thet're an assault unit so the pistols won't get many shots in.
Drop them all and use the points elsewhere.
Use the points for demonic possesion and extra armor as suggested.
Alternatively, you could have more zerkers. Not enough for a full squad though. You could trim down the other squads to give yourself four slightly smaller squads. If you ran say 3 nine man squads with rhinos, you could get an extra squad of nine, but without a transport.
Or run eight man squads. Four eight man squads all in rhinos, you'd be able to get extra armor for the transports and possibly possesion for the vindicator as well with the saved points and you get an extra 2 zerkers in the list. Also, it means there are more transports to destroy, making it more likely your zerkers will reach the enemy.