While I understand that chargebacks, or the lack thereof are an important feature for encouraging merchants to adopt bitcoin, the reverse may be true for consumers.
There is probably a balance to be found, but is such a thing even possible?
You could use 2-of-3 outputs to do this, where the third key is held by a trusted mediator.
A merchant could consider himself paid when the 2-of-3 transaction is confirmed. In the normal course of events the 'chargeback period' would expire and the mediator and merchant would send the money to the merchant's normal address.
If the customer requests a chargeback before that, then either the merchant would agree or the mediator would step in and perform the chargeback according to whatever policies it sets.