In nowadays CAD environments for integrated microwave circuit design, dedicated tools for the implementation of user defined component models are becoming more and more important. These tools are mainly oriented to the definition of equivalent circuit models. However, the need for more accurate prediction of nonlinear electron device performance pushes the modelling community towards the research of new, often nonconventional, modelling approaches (e.g., frequencydomain, behavioural, integral models, look-up-table based, state-space based, etc.). In such a context, the model implementation tools usually available may result not sufficiently flexible. The paper provides useful hints and points out the main limitations which can be encountered in the implementation of non-conventional electron device models. As an example, the implementation of a Nonlinear Discrete Convolution model will be considered by using three different advanced tools: the Model Wizard of AWR Microwave Office, the Model Development Kit and Verilog- A Language of Agilent ADS.