This is incorrect- past consideration relates to payment being in the past, not services in the past.
Contract law requires consideration to pass between the parties in return for a promise- when you purchase a paper, you pay for it. Past consideration means relying on previous payments as good and full consideration for a current or future contract, and there appears to be no way around this in the law of contract.
However, looking more closely, you are able to assign this by way of deed, and this can be used as a rather complicated way of avoiding problems associated with past consideration.
Williams v. Roffey, however, seems to go against the rule of past consideration, as it was held in this case that the change of contract could take place as the change "obviated a disbenefit"- essentially, that the receiving party was better off for the change.