Here is a freebie...and you can get it to work for the entire party, not just the weak-willed.
1. Find a 9th level cleric (preferably a party member to be free, otherwise you have to pay for some 5th level spells).
2. Ask him to cast "Mark of Justice" on you so that if you try to harm a party member (as designated by red hats or tattoos or something) you get cursed.
3. Try to convince the GM to make the curse take effect by affecting you with a Sleep spell, otherwise choose the only acts 50% of the time option.
4. Sit back and laugh at the bad guys when their incredibly evil plan of mind controlling the party brick ends with the brick falling unconsious as soon as he is given an order to "Kill your friends!"
DS