"LibSVM: how to calculate MSE from confidence?"

I'm using the LibSVMlearner process for classification (C-SVM), and I'd like to make use of the likelihoods determined via Platt scaling.  I assume these are output via the "calculate-confidences" option.  I'd like to calculate the mean squared error between these likelihoods and the target.  I'd then like to use these as a performance metric, perhaps via the Data2Performance process?  Can someone give advice on 1) how to calculate the MSE when the confidences are calculated, and 2) how to use the result in Data2Performance?

Many thanks.