I want to create my own design matrix with onsets having different amplitudes (instead of just a vector of ones). This you can't do in SPM, at least I don't know how to. So in nipype I just set the the conditions, names and durations to  or None in the Bunch object, and instead inserted the preconvolved design matrix as extra regressors. The problem is that these aren't interable and that's exactly the error I get. Is there a way to get around this or do I have to edit the code?