Creating a new Type Name to be used with Variables

I am having troubles defining custom data types in a workflow and would appreciate it if someone can give me some advice. To create a new variable in an activity, the "Type Name" has to be selected from the existing data types. It is possible to import a custom class using "Windchill classes", so I tried using the com.acme.Pet (from the tutorial) but this only shows the label and there is no field to assign the value to. How can I specify the type of the value? If I want to have a dropdown, like for the wt.org.WTUser, with dog, cat and Gerbil, how should I proceed? 

Thank you for your help in advance!