Given the selection mechanism, I'd be tempted to try a blind strategy. "I'm not going to look at my ball before I pick it, but if you split and I steal, I'll give you half the money."
It wouldn't be good against a pure money-maximiser, because his expected $value is higher for steal (1/2 versus (1+P(I'm honest))/4), but if he's risk-averse and trusting it might work out.