This may be old, this may be common sense to some or just theory, I've never tested it but I think this should work.
Find a person who has a save to a raid instance such as TK, SSC or whatever (recently I've seen in the trade channel people selling saves). Then you need to move out to that instance and be near the entrance. Once there, you invite the person to your party (many will accept without asking questions, its only an invite ,duh) you need to convert the party to raid and promote him to leader, once thats done you can enter the instance and you will have that person's save.
This should better be done by your 24 ppl raid to steal rival guilds instance save's .
Also, since I didnt test this, I dont know about any kind of punishment for this if you get reported, this IS game mechanics after all