Free Poker -- How tight?

[Benman]

I've found an online bonus situation where I can play pot limit hold'em and I'm getting more money just to sit there and fold than I'd be paying in blinds. Assume that I'd be happy (though bored) to just sit there and take my small amount of free cash, with no variance to speak of. Question--when, if ever, should I voluntarily put money in the pot? Only when I get a free play in the big blinds and flop a great hand? Only with AA and KK? I'm not sure if there's really any theory here to speak of, or whether this is more of a psychological question. In any event, it's a real situation I've found myself in and I'm wondering the best way to approach it.