Ident can estimate models of any structure, supported by the System Identification Toolbox. Select Paramatric Models in the pop-up menu Estimate in the ident window, and chose By Initial Model in its Model structure pop-up menu.
Enter the name of any model structure in the Initial model: edit box of the Parametric Models dialog and then press the Estimate button. The method is a standard prediction error/maximum likelihood approach that iteratively searches for the minimum of a criterion. Options that govern this search are accessed via the Options button in the Help topics.
(file iduibn.htm)