Calling customizer method from web designer


In version 8.1.3 I'm trying to call the customizer method "AssignDirect()" using the web component Object Method , but this method is not available for the table PersonHasTsbAccountDef , it does not appear in the "Method Name" combobox for this web component. However I can call it using the Object Browser, going to the table PersonHasTsbAccountDef, selecting a specific record , right click -> Methods. 

How can I call it from the web designer? The goal is to mark an account definition as direct so it wont be deleted after I cancel the corresponding pwo that assigned it to an user (I need to reuse the account for another user).