Simply set moment as the filtering function and you're good to go. At least one argument is expected, which the filter assumes to be a format string if the argument doesn't match any of the other ...
Neri, P. Depalle, R. Badeau, "Laplace State Space Filter with Exact Inference and Moment Matching," IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP), pp. 5880-5884, ...