Set only the last classifier via template option

The template option is great to define specific estimators, e.g.,
*Selector-Transformer-RandomForestClassifier*

This would ensure that a RandomForestClassifier is chosen as the last step. However, the first two steps are fixed. Is it possible to do something like

*-RandomForestClassifier*

so all previous steps are completely flexible? If it is not possible right now, is there a pointer to start working on this functionality (which function)?

Thanks as always!