Ok, Just came accross this one today so forgive me if its a well known technique.
Gather up three friends and all agree to play POTC capture the flag as a team and follow these rules.
Split up into 2 teams of 2. Both teams get the other teams flag, and take turns returning it to base. (Both teams will have a flag, one will score, the other will get the bonus points for having the flag alternating each round.)
This results in 3 rounds with maximum flag credits. Alternate the winning team each game to keep it fair. All players will come out way ahead and will also earn a steady supply of keys in the process...