From: Stefan Andreevski on
Hi Anthony,

You should use "predict" function with k=1, given the definition of residuals provided by Mathworks:
Residuals are differences between the one-step-predicted output from the model and the measured output from the validation data set. Thus, residuals represent the portion of the validation data not explained by the model.

I've got a nicer idea though.
Why don't you just write:
edit resid.m
and comment the lines used for plotting or create an additional parameter to surpress plotting. You might create a new function resid1.m in order to preserve the old one.

Well, hope this would help.