General steps to create a new soft-type and then assign it to a Data Type in Windchill. Hope this helps... 
1) Did you 1st create the soft-type (IBA) in an Organizer using "Manage Global Attributes"? Suggest you do this in the "Site" context of your Windchill system.
2) In Type Manager:
a) Select your new sub-data type for WTPart.
b) In the sub-data type, click "Action" and then select "Edit" from the drop down list.
c) Select "Create new attribute",
i) Enter the name of the new attribute
ii) From "Type" radio buttons, select "Global"
iii) On the "Choose Global Attribute" GUI, select the soft-type from the Organizer.
iv) Click "Save".
d) Save your changes.
After completing these steps, the new soft-type shall now be assigned to your sub-type of WTPart in your Windchill system.
Now you can "Edit" the sub-type and change the "Layouts" to include or not include your new soft-type. (Assuming Windchill 10 or 10.1 or 10.2)
